Microwave makes loud buzzing or humming noise during operation, louder than usual.

Safety: Unplug the microwave before inspection. High-voltage components are dangerous.

Initial checks:

• Remove the glass tray and roller ring, then run a short test. If noise decreases, the issue may be with the turntable motor or tray components.
• Listen to identify whether the noise is from the bottom (turntable), back (transformer), or side/top (fan).

Internal inspection (qualified DIYers):

• Remove the outer cabinet and check that the transformer and magnetron mounting bolts are tight.
• Inspect the cooling fan for debris or bent blades rubbing against the shroud.
• If the noise is accompanied by poor heating, the magnetron may be failing and should be replaced by a professional.

Note: A loud, harsh buzzing with no heat often indicates a shorted high-voltage diode or magnetron and requires professional service.