Our Whirlpool Gold over-the-range microwave (10yrs old this month) has started making a terribly loud humming/buzzing noise whenever we try to cook with it. All controls, turntable, light and timer are functional (no codes flashing, etc). I tried heating a bowl of water for 20 seconds; unit does not heat, just makes the loud buzzing and interior smelled "burnt". My husband is an electrician and we would rather repair than replace. Should he test the power diode, the magnetron, or the high voltage capacitor first? Thanks for your help on this one.

Thanks so much, it was the magnetron after all!