The situation when in the refrigerator knocks, often takes you by surprise, especially if the equipment has been operating silently for years. Extraneous sounds can range from a slight occasional clicking sound to a loud metallic clang that frightens household members. It is important to understand that not every sound indicates a breakdown: modern models with the system No Frost often produce characteristic clicks when the thermostat is operating or defrosting.
However, an obsessive knock cannot be ignored, as it may indicate wear of mechanical components or a violation of operating rules. In this article, we will analyze in detail the physics of the processes occurring inside the camera and find out when noise is normal and when professional intervention is required. You will learn to distinguish the sounds of a working compressor from problems with the fastening of the units.
The first thing you need to do when noise appears is to listen carefully to its nature and localization. Bosch refrigerators, Liebherr or Indesit may have their own design features, but the basic principles of operation are similar. The knock can come from above, below, behind or from inside the freezer, and it is the location of the source that often suggests the cause of the malfunction.
The physics of noise: normal operation or breakdown?
Many owners begin to panic when they hear the first loud sound, but technology is a complex system where moving parts inevitably create vibration. It is considered normal compressor hum, which either subsides or increases, as well as the quiet murmur of the refrigerant in the evaporator tubes. If you hear a distinct knock, similar to hammer blows or falling metal objects, this is a signal to check.
Often the reason lies in a banal imbalance. If the refrigerator is not installed level, vibration from the running motor is transmitted to the body and amplified, creating a resonating rumble. It is also worth checking whether the rear grille of the condenser is touching the wall or furniture, since during operation it heats up and expands, which can cause knocking.
⚠️ Attention: If the knocking is accompanied by a lack of cold in the chambers or too frequent turning on of the motor, it is better to stop operation until the reasons are clarified, in order to prevent the compressor from permanently failing.
There is a concept of “thermal knock”, which occurs due to the expansion and contraction of plastic parts of the inner lining when the temperature changes. This is especially true for models with a large number of plastic elements. This sound is usually heard at regular intervals after the compressor is turned off and does not require repair.
Diagnostics of the compressor: the heart of the refrigerator
The compressor is the noisiest component in the refrigerator, and it is its operation that is most often suspected of malfunction. If the knocking noise comes from the rear below, where the motor is located, and has a metallic, ringing character, there may be a problem with the mounting of the unit itself or its internal valves. In modern inverter models, noise is kept to a minimum, while older linear compressors can operate quite loudly.
One of the common causes of knocking is wear or drying rubber shock absorberson which the motor is suspended. Over time, the rubber loses its elasticity, and the metal begins to beat against the metal of the frame when starting and stopping the engine. Replacing these gaskets is a simple procedure that can often be done independently by selecting similar sized parts.
A more serious situation is if the internal mechanism of the compressor is knocking. This may indicate a breakdown of the valve group or destruction of the suspension inside the sealed casing. In such cases, it is usually necessary to replace the entire unit, since opening and repairing the sealed casing is economically impractical and technically difficult.
How to check the serviceability of the compressor?
For initial diagnostics, carefully (observing safety precautions) place your hand on the body of the operating compressor. If the vibration is transmitted too much to the hands and is accompanied by rattling, the problem is most likely in the mounting bolts or shock absorbers. If the motor heats unevenly or makes intermittent knocks when trying to start, this is a sign of internal failure.
It is important to note that when starting, the compressor always makes a louder sound than during stable operation. This is due to a sharp surge of current and the start of movement of the pistons. If this starting jerk is accompanied by a single strong blow, check whether the motor housing itself is loose on the frame.
Problems with fans in the No Frost system
In refrigerators with the system No Frost fans located in the freezer and refrigerator compartments are responsible for air circulation. If you hear a rattling noise that sounds like a propeller hitting leaves, or an intermittent knocking sound, this is most likely the problem. The blades can become deformed due to time or ice freezing.
Often, fan knocking occurs due to the freezing of the “coat” on the evaporator. Ice can partially block the rotation of the blades, causing them to begin to touch the edges of the plastic box or the ice build-up itself. In this case, it helps to completely defrost the refrigerator within 24 hours, which will allow the ice to melt and free the mechanism.
If defrosting does not help, it is necessary to inspect the fan bearing. When the lubricant dries, the shaft begins to play, which causes beating and a characteristic knocking sound during operation. In such cases, it is better to replace the entire fan, since it can be difficult to find an original bearing of a suitable size.
It is also worth checking whether a foreign object has gotten into the rotation zone of the blades. A piece of food bag or label caught in air flow can create a rhythmic knocking noise that can easily be eliminated by simply removing the debris.
Burst plastic and thermal expansion
One of the most common, but frightening, causes of knocking is cracking plastic. The inner walls of the refrigerator and freezer are made of impact-resistant plastic, which contracts and expands during sudden temperature changes. This process is accompanied by sounds reminiscent of gunshots or knuckles hitting the table.
Most often, such sounds occur immediately after loading a large amount of warm food or after defrosting. Plastic “walks”, and if there are microcracks or stresses from casting in its structure, they can manifest themselves in the form of loud clicks. Usually, over time, when the temperature stabilizes, the sounds stop.
However, if the crack in the plastic is deep, it can lead to depressurization of the internal circuit or destruction of the thermal insulation. Visually inspect the walls of the chambers: if you see diverging seams or deep chips, you should think about repairing or replacing the damaged panel.
| Type of sound | Probable cause | Urgency of repair | Localization |
|---|---|---|---|
| Metal clanging | Wear of compressor shock absorbers | Average | Rear, below |
| Crackling/Crunching | Ice freezing on fan | Low (defrost required) | Inside the chamber |
| Loud click | Thermal expansion of plastic | Not required | All over perimeter |
| Knock when starting | Malfunction of the start relay | High | Rear, near the motor |
The influence of incorrect installation on the noise level
Even a perfectly working refrigerator will knock and vibrate if it is installed incorrectly. The main enemies of silence are uneven floors and the lack of clearance between the back wall of the equipment and the furniture. The vibration generated by the motor is transmitted to the floor and resonates, increasing significantly.
Be sure to use a building level during installation. Adjusting the height of the legs allows you to compensate for uneven floors. The front legs are often made slightly higher than the back ones so that the door closes by itself under the influence of gravity, but skewing to the sides is unacceptable.
Also check that the refrigerator pipes do not touch the walls or cabinets. The compressor vibrates during operation, and if there is an obstacle behind it, a constant rattling knock will be heard. The optimal distance to the back wall is at least 5-7 cm for free air circulation.
☑️ Checking the installation of the refrigerator
If the floor in the room is wooden or has a weak structure, vibration from the refrigerator can be transmitted to the entire room. In such cases, it is recommended to place special anti-vibration pads made of thick rubber or felt under the legs.
Foreign objects and contents of the chambers
Before looking for a breakdown in the bowels of the equipment, look inside the chambers. Often the source of knocking is glass jars, bottles or dishes that are unstable. When the compressor operates or the door is opened, they can move and hit each other or the walls.
Particular attention should be paid to shelves and drawers. If your freezer's plastic drawer has a crack or broken guide, it may rattle when the frame vibrates. The same applies to glass shelves: if they do not sit tightly in the grooves, they need to be corrected or a soft gasket placed under them.
Sometimes small objects (coins, lids, toys) can get into the gap between the back wall and the refrigerator body, especially if there are children or animals in the house. A dropped object may fall into the fan operating area or simply rattle from vibration, creating the illusion of a serious breakdown.
⚠️ Attention: Never try to remove a foreign object from the fan or compressor area without disconnecting the refrigerator from the power supply. The rotating blades can cause injury and the capacitor on the back wall carries high voltage.
Also check the magnets on the door. If there are too many of them or they are heavy, they may rattle when you slam a door or vibrate. Remove unnecessary decorative elements and check if the noise has disappeared.
When you need to call a technician: critical symptoms
There are a number of signs in which self-repair is not only useless, but also dangerous. If knocking in the refrigerator is accompanied by a complete lack of cold, swelling of the back wall or a burning smell, immediately turn off the appliance and call a specialist. This may indicate a freon leak or an interturn short circuit in the compressor winding.
Hydraulic hammer in the system is another dangerous cause of noise. If you hear sounds like a hammer hitting the pipes, air or moisture may have entered the system, preventing refrigerant circulation. Professional vacuuming and recharging of the system is required.
It is also worth contacting the service if the knocking noise appears after a power surge. The start-up relay could have failed or the compressor itself could have suffered damage to the windings. Diagnostics with an electronic tester will help to accurately determine the condition of the electrical circuit.
Is it possible to temporarily use a knocking refrigerator?
If the knocking is caused by thermal expansion or objects inside, it is possible. If a compressor or fan is knocking, short-term operation is acceptable, but prolonged operation will lead to accelerated wear. In case of strong clanging and vibration, it is better not to take risks.
Remember that timely diagnosis helps save significant money. Replacing a worn fan or shock absorber costs much less than replacing a burnt-out compressor or restoring the system after a leak.
Why does a refrigerator knock only when starting?
A knocking sound when starting is most often associated with the start relay or the starting jerk of the compressor. If the shock absorbers are dry, at this moment a metal-to-metal collision occurs. This may also be a sign that the piston group is worn out and has play, which is selected at the moment of movement.
Is it dangerous to ignore the knock of the fan?
Yes, it is dangerous. If the fan continues to operate with extraneous noise, its bearing may be completely destroyed, which will lead to jamming of the motor and overload of the electrical network. In addition, impaired air circulation will cause uneven cooling and ice formation.
Can a new refrigerator knock?
A new refrigerator may make sounds of thermal expansion of plastic and clicking thermostats - this is normal. However, a metallic knock or strong vibration in new equipment is unacceptable and may indicate a defect during transportation or a factory assembly defect.
How to distinguish the knock of a compressor from the noise of a fan?
The knock of a compressor is normal, dull and coincides with the cycles of turning on the motor (humming). The fan noise is higher frequency, similar to a crackling or rustling sound, and often depends on the opening of the door (in some models the fan stops when opened).
Do you need to change the compressor if it starts knocking?
Not always. First you need to check the mounts and shock absorbers. If the knocking comes from inside the pressurized unit (destruction of the engine mount), then replacing the compressor is inevitable, since this unit cannot be repaired under domestic conditions.