Humming noise during operation:
It is normal for the unit to produce a humming noise during operation. The humming noise is the result of the power supply switching the magnetron on and off.
Humming noise from fan:
It is normal for the unit to produce a humming noise while the microwave oven's cooling fan (on some models) is on.
- The microwave oven's cooling fan, which is separate from the vent fan, automatically comes on during microwave oven operation to cool the microwave oven.
- It may also automatically come on and cycle on and off to cool the microwave oven's controls while the cooktop below is being used.
The fan may run for up to 10 minutes to cool the microwave oven.