My amp was acting up in a way I've never experienced. Maybe you guys can help diagnose it. After powering up at the gig last night, my amp (Savge Rohr 15) started making a high pitched whining/squealing sound. It sounded like high pitched feedback going through a tremolo set for low intensity and high rate. The sound was fairly quiet - you didn't notice when actually playing. The sound got louder/quieter as I adjusted the amp volume or the guitar volume. It went away when I unplugged the cable from the amp input. It got louder when I clicked on my OD pedal. The noise appeared regardless of which channel I was plugged into (this amp has 4 inputs). To isolate the problem, I bypassed all effects and plugged sraight in. I swapped cables to exclude that possibility. I bypassed my attenuator. I plugged into various of the 4 inputs into the amp. When a cable was plugged into the amp input, I could make the squeal happen by touching the other end of the cable. But when I wasn't touching it, the sound went away. The noise happens in response to input signal. But as I said, I could play over the noise. I just dealt with it and played the gig as usual. Tube issue? The amp was working fine at a gig the previous night. Anybody experience this before? Any ideas for isolating the problem? The amp is at the venue now and I plan to play again tonight. Maybe there is something I can check/fix before the gig tonight.