Microwave makes burning rubber smell

Hi Everyone,

I have a GE profile PT970SR3SS Electric Convection Wall Oven with Built-In Microwave. The microwave seems to work fine except it makes burning rubber smell. It just happened very recently and I now stop using it. I detached the microwave from the combo and open the side panel cover. However, I don’t see any parts having burning marks. Electric outlet on the wall looks fine also. I guess some microwave part is going to be bad. Any idea what could be wrong?

Thanks,
George