Well, I just got my new amp Labor Day (an Ampeg BA115), and the tweeter is making a constant migrain inducing hissing sound. I cut the highs and it was still there. So I cut everything to zero and it was still there. I can't find a way to get rid of the hissing short of turning it off, and I need to play for people tomorrow.

Any suggestions? Thanks in advance, sorry if the answer is obvious.