I have a Kitchenaid microwave/ oven compo. It is the Superba model. The microwave is making a noise when I turn it one and is not heating. This noise is sort of a load humming noise. What should I check and how can I fix? I have another unit that I picked up for parts for free that is fully working. Can remove parts from it if need be. Don't want to totally replace the unit as the free one is not is as good of cosmetic condition inside or out but does work good.

Steh, August 2011