While microwaving some food this morning, my wife reported an issue with our built-in.

When the door is closed (and it is not on), a buzzing is very audible, the microwave seems to be heating (but not normally) and a slight burnt smell is detectable.

Leaving the door open is the only way (beyond cutting power to the device) for it to not exhibit the symptoms above.

I am in no way familiar with MW repair (beyond cosmetics like the handle, gasket, etc) and would seriously appreciate any help/guidance.

Thanks in advance.