I bought a used (like new) FI from a fellow TBer a while back. When I used it at home it was a little noisy but I thought it was probably the old wiring in my home. This past weekend I tried to use it on a couple of gigs and couldn't because it was so noisy - kind of a hiss and the sound men shut me down. All my cables are good and none of my other amps or pedals have this problem. Has anybody else had this problem? Solutions?