Diagnosis
Loud humming indicates a failing magnetron or a vibrating component. Buzzing can be from the high voltage transformer or a loose part.
How to Fix It
Identify the noise source. Check for loose screws on the outer case or internal shields. Tighten all fasteners. Inspect the magnetron cooling fan for obstructions. Clean any debris.
If That Didn't Work
The high voltage diode or capacitor may be arcing. Replace these components if they show signs of damage.
Heads Up
Continuous loud noises can precede component failure. Discontinue use if the noise worsens to prevent safety risks.