Microwave runs but makes a loud humming or buzzing noise, louder than normal, sometimes accompanied by a burning smell.

Critical safety warning: Loud humming from the HV section can indicate imminent failure. Unplug the microwave immediately if you smell burning or see smoke.

• Do not continue to run: Further operation can cause more damage or fire.
• Visual inspection only:
  • Unplug and remove the outer cabinet.
  • Check that the transformer and magnetron mounting bolts are tight.
  • Look for burn marks or melted insulation.

Replacement of the magnetron, transformer, or HV diode in Black+Decker microwaves should be done only by a qualified technician due to high-voltage hazards.