We have a Magic Chef, two years old, that still heats OK, but makes a lot of extra noise. It is easy enough to open up, and I did discharge the high voltage capacitor, and remove the high voltage diode, so I could test it. The diode is good, the wiring looks good, and I can't find anything wrong with the fan or the turntable drive. I am reasonably sure that the magnetron is the source of the problem, but the economics of repair don't work out in this situation. A new, similar microwave oven sells for about 100 dollars. There is a nearby appliance service company, that does not have a fixed base, they only want to send out a service tech to our house, and the minimum service charge is 45 dollars. Add in the cost for parts and labor, and it makes no sense to repair this unit. I am wondering how anybody can make any money selling a new microwave oven for 100 dollars.