The situation when something is knocking in the refrigerator often causes panic among owners of household appliances. A sudden metal clang or rhythmic knock can disrupt the idyll of home comfort and make you think about expensive repairs. However, these sounds do not always indicate a critical breakdown. In modern refrigeration equipment, especially in models with a No Frostsystem, the presence of background sounds is part of the work process. Understanding the nature of these noises will help you distinguish the normal operation of the unit from the harbingers of a serious malfunction.
The first thing you need to do when you hear a knock is not to run to the technician’s phone, but to listen carefully to the nature of the sound. It can be voiceless, voiced, periodic or constant. Often the source of extraneous noise is the housing itself, which expands when the temperature changes, or improperly installed dishes inside the chambers. In other cases, a knocking noise may indicate wear on the compressor parts or a foreign object entering the fan rotation area. Competent initial diagnostics will save you time and money, allowing you to fix simple problems yourself.
In this article we will analyze in detail all the possible causes of knocking in refrigerators of various brands, from budget models to premium ones. Liebherr i Bosch. You will learn how to distinguish the operation of the thermostat from a faulty start relay, why the compressor is humming, and what to do if the refrigerator begins to rattle after transportation. We'll look at the mechanical, electrical, and design causes of noise so you can confidently identify the source of the problem.
Natural Sounds of Refrigeration Equipment
Many users mistakenly believe that a working refrigerator should operate in absolute silence. This is wrong. The cooling process is associated with the movement of refrigerant through the tubes, the operation of the compressor and the circulation of air. Normal operating noise often described as a quiet gurgling, hissing or slight flow of liquid. These sounds are caused by the physical properties of freon, which, passing through the capillary tube and evaporator, changes its state of aggregation. If you hear “bubbling” inside, this is most often a sign that the system is working correctly.
Particular attention should be paid to refrigerators with the system No Frost. They have a fan installed that forcibly circulates cold air through the chambers. Periodic wind noise or a slight hum of the fan motor is a normal situation. In addition, such models have an automatic defrosting system. When switching modes (heating the heating element or stopping the compressor), the plastic parts of the housing and internal panels may make cracking or clicking noises due to thermal expansion. This effect is especially noticeable in new devices or after a sudden change in temperature.
⚠️ Attention: If the knocking is accompanied by vibration that is transmitted to the floor or walls, check the stability of the installation. Often it is not the mechanism that “knocks,” but a poorly adjusted refrigerator leg, which resonates with the operation of the motor.
It is important to distinguish between a background hum and sharp, shock-like sounds. Normal operation of the compressor is accompanied by a smooth, monotonous hum. If you hear rhythmic blows that resemble a jackhammer or loud metal clanging, this is beyond the norm. You should also be wary if the noise is accompanied by a burning smell or excessive heating of the housing in the motor area. In such cases, you cannot ignore the signals from the equipment.
Mechanical reasons: vibration and contact with surfaces
One of the most common causes of knocking is simple vibration. During operation, the compressor creates vibrations that are transmitted to the housing and then to the floor. If the refrigerator is not level, these vibrations intensify, causing rattling and knocking of the legs on the cover. Gaps between the refrigerator body and nearby furniture or wall can also be a source of sound. Even a millimeter distance can lead to microdisplacements of the unit during the cooling cycle causing an impact on a hard surface.
Inside the chambers the situation can be even more prosaic. Glass shelves, drink bottles or pots placed close to the back wall or to each other begin to knock at the slightest vibration. This happens especially often when the compressor starts or stops, when the amplitude of oscillations is maximum. Checking the internal contents is the first step in diagnosis. Make sure that there is a gap between the food and the walls, and that the shelves are tightly fixed in the grooves.
- 🔨 Refrigerator legs: Check the adjustment screws. They should fit tightly to the floor, ensuring a stable position without distortions.
- 🧊 Trays and shelves: Make sure that the glass shelves do not hang in the plastic guides. If necessary, add a thin layer of soft material.
- 🍾 Products: Tall bottles or wobbly dishes may fall or hit the walls when vibrated.
Another important aspect is the condenser pipes on the back wall In some models they are located close to each other. When the compressor is operating, the pipes may vibrate and touch, producing a characteristic metallic ringing or clanging sound. By carefully straightening the pipes with your hands (only with the refrigerator turned off and cooled down!), you can eliminate their contact and stop knocking. Be careful: copper pipes are easily damaged, which will lead to freon leakage.
☑️ Diagnostics of mechanical knocking
Faults of the compressor and start relay
The heart of any refrigerator is the compressor. It is this that creates the pressure necessary for the circulation of the refrigerant. If you hear a loud knocking noise coming directly from the motor located at the lower rear of the unit, this may indicate a serious problem. One of the common causes is wear of internal engine parts or imbalance. In this case, the motor shaft begins to hit the housing, creating a rhythmic metallic clanging sound, which intensifies with increasing speed.
Often a knocking sound when starting the refrigerator is caused by a faulty start relay. This small element is responsible for starting the compressor engine. If the relay contacts are stuck or the mechanism is worn out, when voltage is applied, a shock occurs, accompanied by a clicking or knocking sound, after which the compressor may not start or may shut down immediately. The characteristic sound “click - hum - click” with an interval of several minutes indicates precisely a problem with the relay or motor windings.
It is also worth mentioning the so-called “inverter” compressors, which are found in modern models Samsung, LG and other brands. They operate differently than traditional linear motors and are usually quieter. However, if the control board or bearings in the inverter fail, a specific high-frequency whistle or knock may occur. Diagnostics of inverter systems requires special equipment and knowledge of electronics.
⚠️ Attention: If the compressor knocks and gets very hot (to the point where it cannot be touched), immediately unplug the refrigerator. Further work may lead to jamming of the motor and a fire hazard.
To check it yourself, you can try to slightly rock the running compressor (carefully!). If the knocking becomes more intense or its character changes, the rubber shock absorbers on which the engine is mounted are probably worn out. Replacing them is a simple procedure, but requires access to the bottom of the unit. If the knocking comes from inside the compressor “pot” itself, then only replacing the entire unit can help, since modern compressors are often made in a sealed housing and cannot be repaired internally.
How to check the start relay yourself
To check the relay, you need to remove it from the compressor and shake it. If you can hear the ringing of the metal core inside (like in a maracas), then the mechanism is damaged and requires replacement. You can also test the contacts with a multimeter - they should close in a certain position. However, remember that a visual inspection does not always give a 100% guarantee, and replacing the relay is often done by elimination, since this element is inexpensive.
Problems with the fan in the No Frost system
In refrigerators with the system No Frost the fan is responsible for circulating cold air. It can be located in the freezer compartment or behind the rear panel of the refrigerator compartment. If you hear a crackling noise or knocking noise that gets louder when you open the door (in some models the fan stops when it opens, in others it starts working more actively), this is most likely the problem. The main cause of knocking is ice freezing on the fan blades or hub.
When ice builds up unevenly, it disrupts the balancing of the impeller. As the fan rotates, it begins to touch the ice crust or the walls of the plastic box, emitting a loud crash, similar to the sound of a propeller caught in a stick. The cause may also be dried out grease in the fan motor sliding bearing. In this case, the sound will be more reminiscent of a dry hum or grinding sound, turning into a knocking sound when the speed is increased.
To eliminate this problem, a complete defrosting of the refrigerator is often required. It is necessary to unplug the unit, empty the chambers of food and leave the doors open for at least 12–24 hours. This will allow the ice to completely melt, including hard-to-reach areas around the fan. If after defrosting the knocking noise disappears, but a week later appears again, it means that the defrost cycle is broken (the heating element, defrost sensor or timer is faulty), and the ice is growing too quickly.
| Symptom | Probable cause | Solution method |
|---|---|---|
| Crackling noise when opening the door | Fan icing | Complete defrosting (24 hours) |
| Constant hum with vibration | Fan bearing wear | Replacing the fan motor |
| Intermittent knocking | A foreign object has entered | Removing the casing and removing debris |
| Whistling and knocking | No bushing lubrication | Lubricating or replacing the bushing |
Case deformation and thermal expansion
The materials from which the refrigerator is made are subject to thermal expansion and contraction. The inner plastic casing and outer metal casing have different expansion coefficients. If there is a sudden change in temperature, such as after loading a large amount of warm food or turning on the Super Freeze mode, the plastic may make loud clicking and cracking noises. This phenomenon is absolutely normal and does not require intervention.
However, if the knocking is caused by deformation of the housing due to improper transportation or mechanical damage, the situation is more serious. If the refrigerator was dropped or hit hard during delivery, the internal bulkheads could become dislodged. In this case, when the compressor operates, vibration will be transmitted to the deformed elements, causing them to collide. You can check this by pressing your hand on different parts of the body during operation. If, when pressed, the knocking stops or changes tone, then the problem is in the geometry of the case or the fastening of the panels.
Sometimes the source of the sound is condensation, which accumulates in the water drainage groove and, freezing, creates ice plugs. When the temperature changes cyclically, the ice may crack or break off, falling into the drainage container with a characteristic knock. This often happens if the drainage hole is clogged with crumbs or mold. Cleaning the drainage with a special brush or soft wire will help solve the problem.
- 🌡️ Thermal expansion: Plastic clicks immediately after turning on or off are normal.
- 🔩 Panel fastenings: Check the screws holding the back cover and internal panels. Weak fasteners cause rattling.
- 💧 Drainage system: Ice plugs in the drainage can make sounds when thawing.
When a call to the technician is necessary: critical signs
Despite many causes that can be eliminated on your own, there are situations when professional intervention is inevitable. If you have tried all the methods (defrosting, leveling, checking the products), but the knocking does not stop, then the problem lies deep in the unit. It is especially alarming if the knocking is accompanied by a lack of cold or, conversely, freezing of food.
A technician will be needed if:
- 🛑 The compressor knocks and immediately turns off without starting.
- 🛑 The smell of burnt wiring or burning is heard rubber.
- 🛑 Oily spots are visible on the back wall (a sign of a freon leak).
- 🛑 The refrigerator works non-stop, trying to gain temperature.
The specialist will conduct diagnostics using pressure gauges to check the pressure in the system, a tester to check electrical circuits and thermal imager for leak detection. Repairing a compressor or replacing a filter drier requires a vacuum pump and a filling station, which cannot be done at home without special equipment.
Preventing noise and extending service life
In order for your refrigerator to operate quietly and for a long time, it is important to follow the operating rules. Inspect the device regularly, at least once every six months. Check the tightness of the door seals. If the rubber is worn out or dirty, warm air enters the chamber, causing the compressor to work more often and more intensely, which increases wear and noise.
It is also important to keep the condenser (grids at the back or bottom) clean. Dust and pet hair settling on the tubes impair heat transfer. The compressor is forced to work longer, overheat and make noise. Regularly vacuuming the back of your refrigerator is excellent preventative maintenance. Do not place the refrigerator close to the wall, leave a gap of at least 10 cm for free air circulation.
⚠️ Attention: Refrigerator models and designs are constantly being updated. If you have a modern model with smart features, some beeps may be part of the self-diagnosis. Check the instructions for your specific model to find out the sound error codes.
Compliance with the temperature regime also affects the “health” of the unit. Do not place hot pots in the refrigerator - this puts extreme stress on the system. A sharp temperature change causes stress on materials and mechanisms, causing deformations and knocks. Allow the food to cool to room temperature before storing.
The myth about lubrication
Many people advise lubricating rubbing parts with oil. Only do this if you are sure of the type of lubricant. Regular engine oil can corrode plastic or rubber seals and become sticky in cold temperatures, making the problem worse. Use only specialized silicone lubricants.
Frequently asked questions (FAQ)
Why does the refrigerator make a loud knock only at night?
At night, the overall noise level in the apartment decreases, and the sounds of equipment become more noticeable. In addition, at night the voltage in the electrical network may stabilize or, conversely, jump, which affects the operation of the compressor. Also at night, the refrigerator may turn on more often to defrost according to a set timer. If the knocking is rhythmic and loud, check to see if the refrigerator is on an empty shelf or cabinet that could resonate.
Can you continue to operate the refrigerator if it is knocking?
If the knocking is caused by vibration, food, or thermal expansion, you can. If a compressor or fan with a damaged bearing is knocking, long-term operation will lead to complete breakdown of the unit. In the case of a compressor, this can result in it jamming and costly replacement. It’s better not to risk it and carry out diagnostics.
Does a new refrigerator make noise during the break-in period?
Yes, new refrigerators can make more noise in the first few days of operation. Compressor parts are ground in, oil is distributed in the system, and materials are adapted to temperature conditions. If after 3-5 days the intense knocking does not subside, this is a reason to contact a service center.
Does the filling level of the chambers affect the noise?
Indirectly - yes. An empty refrigerator may cycle more frequently because the air cools faster, but it also cools down faster. A completely clogged refrigerator causes poorer air circulation, which can strain the fan. Optimal filling is about 70%, which ensures a stable temperature and minimizes changes that cause thermal expansion and knocking.