Microwave makes loud buzzing or humming noise when cooking, louder than usual, sometimes with vibration.

Safety: Unplug the microwave before removing the cover.

• Identify noise source: Run the microwave briefly with a cup of water while listening carefully (do not touch internal parts). Then unplug and remove the cover to locate the area of noise.
• Check transformer mounting: Ensure the high-voltage transformer bolts are tight and that any rubber isolation mounts are intact.
• Inspect magnetron: Look for loose mounting screws or damaged cooling fins. Tighten screws if necessary.
• Check cabinet panels: Tighten any loose screws on the outer case and front frame that may cause rattling.
• Turntable motor: If noise is from the base, inspect the turntable motor and coupler for wear.

If the noise is accompanied by burning smell or poor heating, stop using the microwave and have the magnetron/transformer tested professionally.