Although refrigerator motors and compressors make noise when they're running correctly, a change in the noise your refrigerator makes could be an indication that something is about to go wrong. The problem could be a costly impending compressor failure, or it could be caused by a relatively inexpensive fan motor.
In a normally operating refrigerator, the compressor, which is typically at the bottom rear of the refrigerator, acts as a pump that compresses refrigerant and keeps it circulating through the system. Even when there's nothing wrong with a compressor, it is relatively noisy, and you'll likely hear it whenever it runs. Some compressors also tend to get noisier as they age, but they continue to function normally.
A failing compressor may make a loud rattling, buzzing noise. A compressor that gets noisy suddenly or that gets steadily noisier over a short period of time may be on its way to failure, however, and should be checked out by a technician.
A more common cause of unusual noise in the area of a refrigerator's compressor is the condenser fan. The condenser fan draws air over the compressor and the condenser coils to keep them cool, and if it fails, the compressor may overheat and fail as well.
A noisy fan might be caused by the fan blades vibrating or hitting something as they turn. To check for this problem, unplug the refrigerator and remove the rear motor cover. Clean the fan blades and remove any obstruction.
If an obstructed fan isn't the problem, the fan motor itself may be failing. A grinding or whining noise that comes from the rear of the refrigerator near the compressor may be an indication that the fan's motor bearings are worn out. In these cases, the fan motor will need to be replaced.
A rumbling, squealing or grinding noise that is louder when the freezer door is open may be a sign of a failing evaporator fan. This fan is responsible for circulation of cool air inside the refrigerator, and if it fails, the refrigerator will not function properly.
The evaporator fan is typically located at the rear of the freezer compartment. To access it, unplug the refrigerator and remove the panel at the back of the freezer. Check the fan blades for obstructions and remove anything that's in the way of the fan's rotation. If there is no obstruction, the fan motor is likely failing and will need to be replaced.