My Gallien-Kreuger Backline 100 transistor amp does that too, and I haven't been able to sort out why! My Ampeg tube amps, and my Peavey Rock Master tube preamps are fine. My transistor amp makes me crazy, because when it works right, it does have a really good sound to it. The tech at the local dealership is under a 4-month backlog, so I haven't brought it in. Then again, if I'm not using it, it might as well sit in the shop.