Microwave buzzing and hot when not in use

Question

My microwave just started making a buzzing noise. It is not in use. Just buzzes until you open the door. Then buzzing stops. The panel on the right (where the food codes are) is really hot as is the glass on the door. It had not been used within an hour so it shouldn't be warm at all. I have turned off the breaker until it can be looked at. What is a possible cause?