Microwaves hum during normal operation, but a new, noticeably louder hum signals a part that's under strain.
Failing Magnetron
A magnetron nearing the end of its life often hums louder than normal while also heating poorly.
Fix: A technician tests it and replaces it if it's failing.
Drive or Cooling Fan
A worn fan motor, or a struggling turntable motor, can produce a noticeable buzz.
Fix: Both motors are straightforward, replaceable parts.
High-Voltage Diode
A diode on its way out can create a loud buzzing sound accompanied by arcing.
Fix: This needs professional diagnosis, including a safe capacitor discharge beforehand.
Not sure what's wrong? Book online — every visit includes a free diagnosis.