I just got a 20-39PC second hand and I've run into some slight problems. Out of the box it worked great but the next time I used it the volume control was having problems and overall output was weak. So I decided to check it out myself and took the amp out. I noticed a terminal clip kind of off kilter so I pushed it back in snugly. The sub's output was back up but after some use I noticed a bit of rattling and "burbling" air during heavy LFE passages, which I determined to be some of the screws being loose (maybe I forgot to tighten one or two of them) and thus leaking air from the amp opening. Things became frustrating when I decided to ensure a snug fit and tightened down the screws - I don't think overtightened. Ultimately I discovered that one screw, if tightened too much (not even snugly) would for some reason cut down the output. After some thought I think the reason may be from uneven pressure placed on the amp plate, which results in a shift of the circuit board connections. Anyone else have any ideas? I'm a little concerned as the problem took awhile to figure out and let's just say the amp is not secured with as many screws as before due to stripped out holes in the box! Has my sub been compromised?