Ice Maker
The ice maker will hum when in operation, making ice cubes and dropping the cubes into the bin. This humming sound should be relatively quiet and will only last temporarily while ice cubes are in production. If there is a loud buzzing or humming sound, make sure the water line is connected to the inlet valve on the back of the refrigerator and the ice maker is turned on.
Fan Speed
Freezer fans, located behind the rear panel, operate to maintain the set freezer temperature. At times this freezer can be audible and may sound like a hum when working. If the noise is very loud or is more of a loud whine than a hum, contact the freezer manufacturer or a service professional as the fan might need to be replaced.
Compressor
A freezer compressor runs up to 90 percent of the time, especially when warm food or large amounts of food are placed into the freezer, to help maintain the temperature. The compressor makes a low humming sound when in use, which might be more noticeable if the compressor is running more often. During hot, humid weather or if the freezer door is opened frequently, the compressor might be audible most of the time.
Condenser Coils and Fan
Sometimes a humming sound can happen when the condenser coils and fan, located in the rear of the freezer, get too dirty and air flow gets restricted. Disconnect the power cord and use a soft brush to clean off the condenser coils and the fan in the rear of the refrigerator, and then restore power.
Dispenser
When the humming noise comes from the dispenser on the freezer door, the dispenser control board is to blame. The control board might be failing or might already have failed. Contact a service professional for assistance.