Ok, got a question from a stupid situation. I've had a Peavey MarkVIII bass head for several years now. It's a series 602 (600 watts into 2 ohms or 350 watts into 4 ohms). A few years back this drummer I was playing with convinced me to try to run 2 18" subs he owned off of the head (not knowing any better I proceeded to do so). I am not too saavy when it comes to watts/ohms/bridged/unbridged stuff. Long story short, the amp no longer produced any volume at all, so I put it in my closet to repair at a later time. Well it's been a few years now and I took it out to our rehearsal spot the other day just to plug it in and see if I remembered the problems it was having correctly. To my surprise it produced sound through my 15" cab. However, it had a slight hum to it. When the Punch/Sustain/Bright buttons were pushed the hum became even louder. Any ideas as to what may have screwed up on this (besides me)?