Microwave makes loud buzzing or humming noise when heating, louder than usual.

Safety warning: Loud buzzing from the high-voltage section can indicate imminent failure. Do not continue to operate the microwave if burning smells or smoke are present.

• Compare with no-load: Run the microwave with a cup of water and listen. If the noise is significantly louder than in the past, stop using the unit.
• Check for vibration: Ensure the microwave is level and not resonating against cabinetry.
• Internal inspection (technician recommended): High-voltage noise issues usually require professional diagnosis of the magnetron, transformer, and diode.