I browsed the forum and did a search but couldn't find what I was looking for.

Anyway, I have a Marshall JCM2000 TSL601 combo that I am thinking about selling, but before I do I want to make sure it's in tip-top shape.

The amp is 3 channel, clean with its own EQ and reverb and gain but no volume, Crunch and Lead with shared EQ, reverb, but their own gain and volume controls.

The problem that I have is that when the master volume is cranked and I am playing on the clean channel (guitar directly into amp, no effects at all and it does it with any of my guitars), there is a loud high pitched whine. The whine stops when I turn the master volume down, doesn't really make much of a difference when I adjust the clean gain control, and if I turn both the master volume and gain down all the way, then slowly turn them back up, I can get the whine to stop sometimes.

Does this sound like any problem you've experience before? Any idea what it could be? Any information you could provide would be great. I'd like to be a little more knowledgable about the problem before I just drop it off to be fixed.
It could be a microphonic pup, try a different guitar. It could also be a microphonic tube. Try tapping the tubes lightly with a pencil eraser and see if you could hear it clearly through the amp.
I don't give a shit if you listen to me or not
I will try tapping with the eraser and see if that makes any difference. If it was a microphonic PUP, wouldn't it whine in any channel? Why would it only do it on the clean channel? Also, as I noted in my original post, it does it with any of my guitars. But thanks for the response and I will check back if the tapping doesn't work!!!