A similar thought occurs to me, which is that one or more of the wall sockets may be improperly grounded, or possibly not grounded at all. It would be worth checking, if only for safety reasons.

Well, that's an interesting observation... Are you a psychic? When I moved in, the electrical outlet that is closest to the cables (about 3-4 feet away, though) had fallen out of the box that it was attached to. I had the maintenance guy come and fix it. I think he would have made sure to ground it if it wasn't, but there's also no guarantee of that....

What could an improperly grounded outlet do to an RCA cable 3 or 4 feet away? I know nothing of electricity except that the lights go on when I flip the switch. Okay I'm exaggerating a little, but although I understand the concept of a device having two paths to earth's ground, I have no idea how to solve the problem, and these guides are too packed with theory and don't really explain how to GET RID of the loop.