Recently, the microwave started making a faint "rattling" noise and the it would automatically cut off after about 5 minutes of use with no power of any kind. It would resume working after about 15 minutes. I no longer hear the sound, but now, when heating items, an excessive amount of steam builds up within the unit that was never there before. The microwave is still heating food properly.

Any suggestions on how to narrow that down?? fan motor is what I would have guessed. The model is an over the stove with built in exhaust fan. I haven't tried to see if that is still working (will try tonight), would that make a difference?