I realize this may not be an electronic troubleshooting forum, but maybe someone can help me out.

I recently inherited a Paradigm sub from my brother who had it in storage for a number of years. It has been shipped around from place to place as he moved from job to job.

As soon as I took it off his hands I hooked it up to my home theater receiver using the LFE output on the receiver and low-level inputs on the sub. The first thing I noticed was that as soon as I plugged the sub into the wall outlet it produced a 60Hz hum. I could adjust the amplitude of the hum with the amp gain control. The sub didn't play any music, but just sat and hummed away.

So I turn everything off and unplugged the inputs, then turned the sub back on. This time I got no sound from the sub (which is good). So I turned it back off, grabbed a different set of RCA cables and connected to the low level right channel input and left the other end in free air. I turned the sub back on and got the hum right away. Then I swapped the right channel input to the left channel input. No change, still had the hum.

At that point I noticed something strange. When I had the RCA cable plugged into the either the left channel, right channel, or both channels, and I put my hand on the back on the amplifier, the amplitude of the hum increased.

Finally I decided to try the high level inputs on the sub, and those seemed to work fine. No hum and music was playing fine.

Well anyway, your thoughts are appreciated.

John