The situation when a habitually humming household appliance suddenly begins to make frightening sounds is familiar to many equipment owners. A sharp knock, periodic clattering or loud gurgling may make you think about urgently calling a technician or even buying a new unit. However, these symptoms do not always indicate a fatal breakdown that requires expensive intervention.
In most cases, extraneous noise is a reaction cooling systems to changes in operation or the result of improper installation. Understanding the physics of the processes occurring inside the chambers and engine compartment will help you distinguish normal operation from a real malfunction. It is important to listen carefully to the nature of the sound and determine its localization.
In this article we will analyze in detail the mechanical, thermal and electrical causes of knocking. You will learn to independently carry out primary diagnostics and understand in which cases the intervention of a specialist is really necessary, and when simple adjustment is sufficient.
Physics of compressor operation and thermal expansion
The main source of noise in any refrigerator is the compressor. This is the heart of the system, which compresses the refrigerant and forces it to circulate through the tubes. Modern models use inverter linear compressors, which are quieter than older piston analogues, but can also make specific sounds when starting or stopping.
An often audible click or thud when the motor is turned on or off is the normal operation of the starting relay. It closes and opens the electrical circuit, ensuring the engine starts. If the knocking noise is repeated frequently and is accompanied by startup attempts that immediately stop, the relay may have failed or a power surge has occurred.
However, the most common cause of “strange” behavior is thermal expansion of materials. The inner walls of the chamber, evaporator and pipelines are made of plastic and metal, which have different expansion coefficients. When there is a sudden change in temperature (for example, after loading warm food or automatic defrosting), materials contract or expand, producing a characteristic cracking or clicking sound.
⚠️ Attention: If a loud cracking sound is heard immediately after the end of the defrost cycle and repeats regularly, this may indicate that the ice in the No Frost system has thawed too quickly and pieces of ice have fallen onto the fan or heater.
It is also worth considering that the refrigerant flowing through the system can cause gurgling sounds. This is especially noticeable in the quiet of the night. If freon moves evenly, such sounds are considered normal for many models, especially with a lower compressor.
Problems with installation and vibration of the case
Often the source of irritating rattling or rhythmic knocking is not the internal filling, but external factors. Vibration from a running motor is transmitted to the body, and then to the floor or nearby furniture. If the refrigerator is not level, this vibration increases many times over.
The first thing you need to check is the horizontal installation. Even a slight misalignment can cause the door to open or slam itself, and the compressor to resonate with the floor surface. For adjustment, screw supports are used at the bottom of the front panel.
The second important aspect is the distance to walls and furniture. The rear grille of the condenser should not touch the wall, otherwise the vibration will be transmitted to the building structures, creating a hum throughout the room. The optimal distance is at least 5-7 centimeters.
☑️ Installation diagnostics
It is also worth checking whether the tubes at the back of the unit are touching each other. During operation, they vibrate, and if the gap between them is minimal, a metallic ringing will occur. By carefully straightening the tubes with your hands (with the device unplugged from the network), you can eliminate this defect.
Malfunctions of the defrost system and ventilation
In refrigerators with the system No Frost i Full No Frost fans are responsible for air circulation. If you hear a growing hum that turns into knocking or grinding, most likely the problem lies there. The blades may touch frozen ice or a foreign object.
The ice in the freezer may accumulate unevenly. If the defrost system works intermittently (the heating element, defrost sensor or timer is faulty), the ice coat becomes too thick. The rotating fan begins to touch the ice build-up, making loud bangs. This is dangerous, as it can lead to breakage of the impeller or burnout of the fan motor.
Another reason for knocking in this area is dried out lubricant in the fan bearings. Over time, the technical lubricant thickens or leaks out, and the bushing begins to run dry. This causes a characteristic creaking and knocking noise, which intensifies as the speed increases.
| Sound type | Probable cause | Localization | Urgency of repair |
|---|---|---|---|
| Rhythmic knocking/crackling | Blade contact with ice | Freezer compartment | High |
| Humming with vibration | Fan bearing wear | Rear wall inside | Medium |
| Whistling or howling | Burn dirty | Evaporator area | Low |
| Sharp clicks | Frozen object | Air ducts | Medium |
To fix the problem, it is often necessary to completely defrost the refrigerator within 24 hours. If after this the sound disappeared, but returned a week later, it means that one of the elements of the defrosting system is faulty, and diagnostics with a multimeter is required.
How to check the fan without disassembling it?
Turn on the refrigerator and open the freezer door. Find the door sensor button (usually at the end) and press it with your finger, simulating closing. If the fan starts and you hear an extraneous sound, the problem is confirmed.
Mechanical damage and wear of components
If vibration and problems with ice are excluded, it is worth considering more serious mechanical faults. The knocking noise may come from the compressor itself if its internal valves or suspension are worn out. In older models, the piston may hit the cylinder if the oil has lost its properties or its level is critically low.
Another source of noise is loose fasteners. Vibration over many years of operation causes the compressor bolts, casing or housing panels to become loose. Metal parts begin to hit each other, creating a chaotic clang.
In models with linear compressors (often found in the brand LGa specific clattering sound may be observed. This is a feature of the magnetic drive. However, if the sound becomes louder and is accompanied by vibration of the entire cabinet, the rubber shock absorbers on which the motor is mounted may have broken down.
⚠️ Attention: Never try to open the sealed compressor casing or change the oil yourself. This requires special equipment and skills, and is also fraught with refrigerant leakage.
It is also worth checking the integrity of the rubber seals on the doors. If they are dry or deformed, the door may slam at the slightest draft or movement in the room. This is not a breakdown of equipment, but a source of constant acoustic discomfort.
The influence of workload and contents of the chambers
Paradoxically, the amount of food in the refrigerator also affects the noise level. An empty refrigerator is louder because the air inside the chambers heats up quickly when the door is opened, causing the compressor to turn on more often. Heavy products act as heat accumulators, stabilizing the temperature.
However, improper placement of objects can cause knocking. If bottles or cans are placed close together or touching the walls, the vibration of the shelves will cause them to rattle. Glassware is especially sensitive to microvibrations transmitted from the compressor through the shelves.
It is important to check that small objects (lids, foil, bags) have not gotten into the gap between the drawers and the body. When drawers move or materials expand, these items can get stuck and make a rattling sound.
It is recommended to place the products so that they do not touch the back wall of the chamber where the evaporator is located. This will not only reduce noise, but also prevent food spoilage due to local hypothermia.
Diagnostics: when to call a specialist
Independent diagnosis has its limits. If you have checked the installation, defrosted the unit and removed unnecessary items, but the knocking noise remains, the problem may be technical. The critical signal is the change in the nature of the sound over time: if a quiet hum is replaced by a loud clang, you cannot hesitate.
Pay attention to the accompanying symptoms. If, along with the knocking, the refrigerator stops freezing, the “fur coat” freezes in one corner, or the body heats up unevenly, this indicates a freon leak or a blockage of the capillary system. In such cases, the refrigerant itself may make a knock, trying to overcome the plug.
The smell of burning in combination with a metallic knock is also an alarm bell. This may indicate overheating of the motor windings or problems with the electrical wiring. In this case, the device must be immediately de-energized.
A professional technician uses a thermal imager to search for leaks, a pressure gauge station to check pressure and a tester to check electrical circuits. These tools allow you to accurately determine the unit that requires replacement, without unnecessary disassembly of working parts.
Prevention and proper care
To extend the life of the refrigerator and maintain silence in the kitchen, it is important to follow the operating rules. Regular defrosting (even for a No Frost system once a year) helps maintain efficient heat transfer and reduces the load on the compressor.
Keep the rear condenser grill clean. Dust and pet hair act as a heat insulator, forcing the engine to work at its limit. An overheated compressor makes more noise and wears out faster.
Do not load hot food into the chamber. A sharp jump in temperature creates a colossal load on the entire system, causing thermal deformation of plastic and metal, which in the future will lead to the appearance of cracks and increased noise.
Why does the refrigerator knock only at night?
At night, the overall noise level in the apartment decreases, and the operation of the equipment becomes more noticeable. In addition, at night the voltage in the electrical network may stabilize or, conversely, jump, which affects the operation of the engine. Also, the heating system operates quieter at night, and the vibration from the pipes can resonate with the vibration of the refrigerator.
Can a new refrigerator knock?
Yes, new models often require time to “break in.” The lubricant in the compressor should be distributed, and the plastic elements should fall into place. If the knocking does not go away after 3-5 days of active use, this is a reason to contact a service center under warranty.
Is knocking dangerous for food?
Sound itself does not spoil food. However, if the knocking noise is caused by a malfunction of the cooling system (for example, a fan stopping or a leak), then the temperature inside the chambers may begin to rise, which will lead to food spoilage. Therefore, you should not ignore changes in the background sound.
Does the brand of a refrigerator affect the noise level?
Of course. Budget models are often equipped with noisier compressors and have less effective sound insulation of the housing. Premium brands use noise reduction technologies and inverter motors that operate almost silently.