i'm getting a just audible woof sound palm muting on the low e string when in distortion. kind of like a horn sound mixed in. i'm not sure if it was there before but somebody thought it was funny to crank the amp all the way up on one channel and down on the other. then he was having fun kicking the footswitch between channels. i'd just got back from the beer run when i found this going on. 
If it's a tube amp, you might just have a blown tube. I don't know. Sounds bad though. Hope it wasn't an expensive amp, and I hope you beat the truth out of whoever was with it while you were out.
I hate people who disrespect gear that ain't theirs.



