The average noise level of modern freezers/refrigerators is under 50 decibels–the sound of a quiet conversation in your home. (Quite often 50 decibels is equated to the noise a refrigerator makes.) If your refrigerator/freezer starts knocking, or making other rude noises, that is no longer true.
Here are some of the causes of knocking freezers, and better yet, what you can do to eliminate the noise.
6 Causes of Freezer Knocking Noise
Freezer knocking noises can originate from a number of sources. Hopefully one of the following suggestions will solve your problem.
For more information on quieting refrigerators/freezers please see our articles How to Quiet a Noisy Refrigerator Compressor and How to Stop a Refrigerator From Making Noise [Buzzing, Rattling, Humming].
1) Knocking Noise Caused by Contact
One of the easiest knocking noise problems to correct is contact noise. Contact noise is caused by the back or sides of the unit touching a wall. As the motor and compressor run, the refrigerator/freezer will vibrate against anything solid. The knocking is continuous as long as the motor is running.
It is simple to fix the problem by moving the refrigerator/freezer away from the walls. Worst case scenario–hang soundproof blankets on the side walls to stop the knocking. The rear of the refrigerator/freezer must be away from the wall and not covered with a blanket because it needs air circulation to cool the coils.
Another area of contact knocking noise is the top of the unit. Not the refrigerator/freezer itself, but hard items like Lego or wooden blocks that end up stored there. They can vibrate when the motor and compressor are running. The knocking sound can be loud and annoying.
2) Knocking Noise Caused by Ice Maker
An ice maker in the freezer can be a great source of knocking noises. Not only will you hear it when adding ice to your glass, you will likely hear the knocking, banging, rumbling sound every time the ice maker empties ice into the plastic container.
In some freezers, this can be an obnoxious noise. About every 90 minutes. There is really no effective way of quieting ice makers except to turn them off or buy a quiet machine. For more information please see our article Quietest Ice Maker.
3) Knocking Noise Caused by Compressor
The compressor is about the only moving electronic part on your refrigerator/freezer, making it and its peripheral parts a noise-making suspect.
- Compressor Start-Up. Compressors are usually bolted onto the freezer chassis with rubber anti vibration pads. Occasionally these bolts will become loose or the pads will become worn. On start-up any knocking and/or vibration noise will transfer throughout the frame. Make sure the rubber gaskets are in good shape and the bolts are tight to prevent the noise. Also ensure that your drain pan (if there is one) is also tight and not rattling.
- Compressor Fan. The fan blows cool air over the condenser and compressor to keep them from overheating. A build-up of dirt on the blades can cause a knocking or weird vibrating hum. While you are lying on the floor checking for bolt tightness, make sure you clean off the fan blades. Not only are clean blades quieter, they help the motor to last longer.
- Compressor Coils. Compressor coils are attached to the back of the refrigerator/freezer and disperse heat as the freon runs through them. The coils and/or anchors can become loose and start vibrating against the back of the cabinet creating a constant knocking noise. Or they are loose and will vibrate against the wall if the machine is too close. While you have the refrigerator/freezer pulled away from the wall, or out of its cubby hole, make sure you grab a screw driver and tighten all the screws holding the coils.
4) Knocking Noise in a Chest Freezer
Chest freezers are, in my experience, virtually silent. You can’t hear either of the 2 we have unless you are standing right beside them. They are completely enclosed with no exposed cooling fins. Ours have grills covering the motor and compressor.
It is not a bad idea to check motor/compressor mountings and clean the fan blades once a year. Not only will will this give you the opportunity to make sure that bolts are tight and anti vibration pads are not disintegrating, you can also check for leaks.
Some chest freezers do not have adjustable feet, making leveling a bit of a challenge. You can buy thick combination cork/rubber anti vibration pads that can easily be cut down to level the freezer and eliminate vibration and knocking.
5) Knocking Noise in an Upright Freezer
Upright freezers are designed like chest freezers with the cooling coils wrapped around the interior compartment just inside the external cover. In manual defrost upright freezers the shelf or shelves are actually made of the coils of the evaporator. In both cases there is no knocking or vibration from the coils.
The only knocking noise, or any other noise, will come from the condenser and motor. It is a good maintenance idea to check them out yearly. It only takes a few minutes to ensure all the bolts are tight, the anti vibration pads are in good shape and you have no leaks.
Most upright freezers have 2 levelling legs under the front corners. When levelling make sure you have a slight tilt towards the rear to ensure the door closes easily. Make sure all 4 points of contact sit solidly on the floor.
6) Knocking Noise Caused by an Unlevel Machine
An off level machine can become noisy. The feet may not be level on the floor or the floor may be off level. Adjust the feet to get as perfectly level as possible, then install anti vibration pads under each one.
Enough vibration can even have frozen food in the freezer making knocking noises.
When to Call a Professional
If you have tried these simple and easy solutions to solve your knocking freezer noise without success, give some thought to calling an appliance repair person to check out the noise.
There is a possibility that whatever is causing the noise may be doing damage to the refrigerator/freezer that will cost you more in the long run.
Whenever you are doing any work on electrical appliances, unplug the machine. Whether you are digging a knife into the toaster to remove a stuck pop tart or working on your freezer’s compressor, get into the habit of disconnecting the power. A tingling shock is not much fun, and there could be much worse.