Ugh, looks like the magnatron is a common problem in this microwave:
http://www.consumeraffairs.com/homeo...magnetron.html
And it looks like a new one (to fit the space & match the stove) would
be $267-$377
http://froogle.google.com/froogle?q=...ff&oi=froogler

Ugh, any one have any ideas?