Hi All, I'm rookie to setting up my system, so please bear with me. I recently moved, and am having problems setting up my entertainment system. The problem is specifically with the sub. It plays for a few seconds/minutes, and intermittent will have a knocking or scratching sound. I've disconnected it from the receiver, and with only power to it, I get the same knocking and scratching sound. Anyone have any ideas as to what is causing this?? Thanks for your help.