Well, my new head finally came today... Unfortunately, there seems to be a problem with the amp... It powers up fine but when my speaker cabinet is attached, it emits a continuous LOUD noise... This happens with everything turned down, with no instrument plugged in, and even with the mute engaged... My cabinet is an older Peavey 300 watt 4ohm 4x10 that works fine with every other head I use it with... Anybody have any clue as to what would cause this???