Well first I realize that one can't really analyze in absentia but I was hoping 'you' might be able to give me some guidance. I just purchased a used very clean Fender Champion 20 which seems to have a strange high pitched tone, somewhat buzzish, but not truly a total buźz, nor a hiss, audible at all levels including total minimum, and from speaker and phones. Painful above 2 on gain or volume. This tone does seem to increase in intensity when boosting treble, though not with bass. And of course it does with both volume & gain. It doesn't increase w. Fx level. I inspected the circuit boards, all solder points look good as do all caps and resistors. No burns anywhere. Ground is tight. (board is dated 2016, maybe 2015) All controls otherwise work as they should. A tech whose ability I can't vouch for thought "the processor " ... Could this be it.? Or a bad power supply? Bad cap (even though they look good, no bulges or burns)? Oh, also the speaker pops rather loudly when powering off even at no volume. So.. any ideas?