A sudden knocking sound in the refrigerator can turn a cozy kitchen into a place of nervous tension. Many owners of household appliances immediately begin to panic, expecting an imminent breakdown or expensive repairs. However, before calling a technician, you need to soberly assess the situation and understand exactly where the sound is coming from.
The noise can be caused by both trivial reasons related to the installation or loading of products, and serious malfunctions of internal components. Diagnostics begins with a careful listening to the unit. The nature of the sound, its frequency and location will help determine whether this is a sign of normal operation or a signal of a problem.
In this article we will analyze in detail all the possible causes of knocking. We will look at the design of the compressor, the operating features of the No Frost system, and even the influence of foreign objects. Understanding the physics of the processes occurring inside the chamber will allow you to make the right decision about further actions.
Natural sounds: when the refrigerator is just working
New models of refrigerators, especially those with inverter compressors, work almost silently, but even they make sounds. Often users mistake normal refrigerant operating processes for knocking. Liquid freon circulating through the tubes may gurgle, hiss, or make quiet clicks, which is absolutely normal.
Periodic crackling may occur due to thermal expansion and contraction of the plastic of the inner housing. When the temperature inside the chamber changes, the materials respond by changing volume. If you hear such sounds after turning the engine on or off, then most likely everything is in order with your refrigeration unit Everything is fine.
It is important to distinguish between a monotonous hum and sharp, rhythmic beats. Natural sounds are usually quiet and do not vibrate the floor or furniture. If the sound resembles hammer blows or a loud clang, you should listen more carefully.
Why are new refrigerators noisy?
New models may seem louder than older ones due to more efficient, but intense operation of the fans and compressor, which increase temperature faster.
Installation problems: external factors noise
Before you climb inside the equipment, check how it is installed. Improper installation is the most common cause of vibrations, which are perceived as knocking. If the refrigerator body is skewed or the legs do not fit tightly to the floor, the running motor will cause resonance of the entire structure.
Use a building level to check the horizontal position. Height adjustment is made using the front legs, which are usually unscrewed with a key or manually. Also check the distance to the walls and furniture: the gap should be at least 5-7 cm for normal air circulation and absence of resonance.
- 🔍 Check whether the side walls of the cabinet or wall are touching, creating rattling.
- 🔍 Make sure that all shelves and drawers inside are firmly in place.
- 🔍 Inspect the back: wires or hoses should not touch the compressor housing.
Sometimes the source of sound is not the refrigerator itself, but objects standing on its top cover. Vases, jars or decorative items may vibrate from the motor. Remove all excess from the surface and listen to the unit again.
Diagnostics of the compressor: the heart of the refrigerator
The compressor is the main engine cooling systems. It is this that creates the pressure necessary for the circulation of the refrigerant. If you hear loud metallic knocking, clanging, or banging noises coming from the lower rear of the chassis, this is most likely the problem. One common cause is wear or breakage. The motor inside the casing is mounted on springs or rubber shock absorbers to dampen vibrations. Over time, these elements dry out, burst or jump off, and the metal casing begins to hit the walls of the casing with each start.
One common cause is wear or breakage. compressor suspension. The motor inside the casing is mounted on springs or rubber shock absorbers to dampen vibrations. Over time, these elements dry out, burst or jump off, and the metal case begins to hit the walls of the casing every time it starts.
Another reason is a malfunction of the starting relay. If the relay fails to start the motor the first time, you may hear a series of clicks followed by a thud and shutdown. This indicates that the engine is trying to start, but cannot turn the shaft.
| Sound type | Probable cause | Urgency of repair |
|---|---|---|
| Loud clanging of metal | Destruction of the suspension motor | High (risk of pipe breakdown) |
| Series of clicks and buzzing | Malfunction of the starting relay | Medium (risk of winding burning) |
| Rhythmic knocking | Tubes getting into the body | Low (can be corrected yourself) |
| Whistling and knocking | Lack of refrigerant | High (refill required) |
If you notice that the compressor operates intermittently, gets very hot or makes unnaturally loud sounds, it is better not to experiment. Intervention in system cooling without experience can lead to depressurization of the circuit.
☑️ Compressor diagnostics
No Frost system: fan and ice
In refrigerators with a No Frost or Frost Free system, the fan often becomes the source of the characteristic crackling or knocking noise. It is located in the freezer compartment (or behind the back wall of the main compartment) and ensures the circulation of cold air.
If a too thick “coat” of ice has formed on the evaporator, the fan blades may touch the ice. This causes a loud cracking noise, similar to a propeller being struck by a branch. Ice can break off and get into the mechanism, creating extraneous noise.
The bearing of the fan itself may also fail. In this case, you will hear an increasing hum and periodic tapping. Unlike a compressor, the fan does not work constantly, but turns on periodically according to a timer or when the door is opened (in some models, on the contrary, it turns off).
⚠️ Attention: If you hear the fan touching the ice, do not immediately try to pick it with a knife or sharp objects. You may damage the blades or touch the evaporator, causing freon to leak. It is better to do a complete defrosting.
To fix the problem, it is often enough to defrost the refrigerator for 24 hours, completely disconnecting it from the network. If after defrosting the noise disappeared, and then appeared again after 1-2 weeks, it means that the defrosting cycle is broken (the heating element, timer or defrost sensor is faulty).
The influence of food and dishes on the noise level
Sometimes the answer to the question “who is knocking” turns out to be prosaic - it’s your supplies. Glass jars, drink bottles or plastic containers may become dislodged when shelves vibrate. Even touching two glass surfaces while the motor is running creates a loud knock.
Check the door shelves. If they are overloaded, then when the door slams or the body vibrates, the bottles may hit each other or the walls of the refrigerator. It is also worth checking that the lids on the containers are tightly closed - sometimes there is a bouncing lid.
- 🥛 Rearrange the bottles so that they do not touch each other.
- 🥩 Check if bags of food are hanging on the door.
- 🥦 Make sure that the boxes for vegetables are pushed in all the way.
Empty shelves can also rattle. Try filling the refrigerator with food - the mass of the contents often dampens the vibrations of the cabinet. If the noise disappeared after loading, then the problem was in the resonance of empty space.
Hydraulic hammer and problems with freon
There is a phenomenon called “hydraulic hammer” in the compressor. It occurs when liquid refrigerant instead of gaseous refrigerant enters the compressor cylinder. The fluid does not compress and the piston makes a loud noise. This often happens immediately after starting the unit.
If the refrigerator stood idle for a long time, or if it was transported incorrectly (placed on its side without observing the time intervals before turning it on), oil could flow into the circuit. When starting, the compressor “swallows” oil and makes a strong knock.
A knock may also indicate lack of refrigerant. Air pockets form in the system, which cause noise when passing through the capillary tube. This is usually accompanied by a deterioration in the quality of freezing and longer operation of the motor.
⚠️ Attention: Water hammer is dangerous for the integrity of the compressor valves. If you hear loud banging noises every time you start, this could cause your compressor to fail quickly. Diagnostics by a specialist is required.
In such cases, independent repair is impossible, since the system must be evacuated and charged with freon by weight. Using the wrong refrigerant or the wrong amount of oil can completely kill the equipment.
Algorithm of actions: what to do when a knock occurs
If you detect a knock, act sequentially. First, eliminate external factors: check stability, remove unnecessary objects, unload the doors. If this does not help, listen to the localization of the sound.
For an accurate diagnosis, you can put your ear against the back wall (be careful, it may be hot there) or use a long screwdriver like a stethoscope, placing the handle to your ear and the tip to different points on the body. This will help you understand where exactly the vibration occurs.
If you determine that the compressor or fan is knocking, evaluate your skills. Replacing the start relay or lubricating the fan is available to the home craftsman. However replacement of the compressor or repair of the defrost system requires special tools and knowledge.
Action plan:1. Disconnect the refrigerator from the network.
2. Carry out complete defrosting (24 hours).
3. Check stability and environment.
4. Turn on and listen.
5. If the knocking repeats, call a technician.
Do not ignore the change in the nature of the equipment’s operation. Timely contact with a specialist can save the compressor from costly replacement. Remember that modern refrigerators are complex devices where one faulty element affects the operation of the entire system.
Frequently asked questions (FAQ)
Why did the refrigerator start knocking after defrosting?
After defrosting, a knock may appear if you were in a hurry to turn on the appliance. Water could get into the electrical parts or the ice has not yet melted in the hidden cavities, and the fan touches the remains of the fur coat. The compressor could also be displaced if the refrigerator was tilted strongly during washing.
Is it dangerous if the refrigerator knocks loudly when starting up?
A single loud sound when starting up may be normal for some models (hydraulic shock of residual oil). But if the knocking is repeated regularly and is accompanied by vibration, it is dangerous. This leads to destruction of the compressor valve group and its eventual combustion.
Is it possible to lubricate the refrigerator fan yourself?
Theoretically, it is possible if you get to it. However, in most modern models the fan is not serviceable. Trying to lubricate it with regular oil (WD-40, machine oil) may cause the oil to leak onto the plastic or into the winding, causing even more problems. It is better to replace the entire assembly.
Does the refrigerator knock if it is empty?
An empty refrigerator may make more noise due to the lack of sound-absorbing mass of food. In addition, in an empty refrigerator, the on-off cycle occurs more often, since the heat capacity of the air is low. Loading the chambers with products usually stabilizes the temperature and reduces the noise level.
How to understand that it is the compressor that is knocking and not the fan?
The compressor works in cycles: turned on, ran for 10-40 minutes, turned off. The fan in the No Frost system can run continuously while the door is open or the fast freezing mode is turned on, or it can turn on together with the compressor. If there is a knocking noise only when the engine is humming, it is the compressor. If there is a knock and when the motor is silent (but the light is on), it’s a fan.