I forgot about the ground switch on the back of the amp. It's in the middle position right now, so would switching it to the negative or possitive side help any? (I'm at work right now and can't try it, so that's why I ask)

Also, for more info., the amp is plugged into a grounded power strip, and the pedals are run off of a Dunlop DCBrick into the power strip, and all of the cables except one being used in the fx loop are fairly new.