HELP high pitch whistle from tube amp

I will try all of the inputs and the outputs before I pop the top...I'll keep you posted. Much Thanks...Neil

First, try swapping all of the tubes from one side to the other. If the noise moves with them, then you will be able to identify the tube by trading them back, one at a time.

Also, try swapping inputs with left becoming right side. Again, this will tell you if it really is the amp. Next, try swapping outputs, which will tell you if the problem is indeed in the amp.

I see you have already tried swapping input selects. Also, remove all but one input and test each at a time.