Unplug each part one a
Unplug each part one at a time. Start with the fan, then run it. If noise still there plug fan back in and unplug magnetron. Short out the cap and have the unit unplugged at this time.
http://www.youtube.com/watch?v=N-ogNZ6UPD8 this video shows you how to short the cap.
Run unit with magnetron unplugged, see if noise goes away. If not unplug cap (short out first).
The last part would be the transformer. So you are just eliminating each part as you go.
the microwave is a GE SCA1000DWW03. Everything works just fine. Only problem is the noise. The noise occurs when I plug in the unit and set the clock, NOT when I start microwaving, so I do not think it is the magnetron or anything to do with the microwave circuitry. I have unplugged the magnetron fan and the noise still occurs. I am pretty sure it has something to do with one of the printed circuit boards, probably the relay board. I am going to try to use a hose to my ear and see if I can identify the noise source.
I am unable to see your response, I do not know why. I will opt out so another tech may help you
Randy, there are two PC boards in the unit, both expensive. I'd like to isolate the fault before spending hundreds of dollars on a parts swap to isolate the problem