Hi, I have a 2xKT88 Marshall Major build with an extra gain stage that creates a fizzy resonance that to the best of my hearing it seems to be coming out directly from inside the OT. It's a 100w Merren ultra linear transformer. I thought it was the spring retainers of the power tubes but I removed them and the fizz was still there. It happens when I turn up both volumes past 3 o'clock, just when the amp sounds the best. I have it connected to a Rivera Rockcrusher at -8dB. I tried replacing all of the tubes but the problem was still there. I also chop-sticked the board to see if I could find the source of the fizz but found nothing wrong. When the extra gain stage is disengaged (it's on a switch), the resonating OT doesn't happen but the amp has no gain, of course. Any ideas on how to fix this? Thanks a lot.