In reply to:
Cable is grounded. House is grounded. But not exactly in the same fashion.
Hence the loop. All the fool needed to do was ground the cable to the same ground that the main electrical panel uses. The reason that there is a loop is because there is a diffenence in resistance between the 2 grounds. Hook them to the same place, and the only possible difference between the 2 grounds would be caused by the wiring inside the house. This would be the electrical ground wires from the breaker to the outlet and the shield of of the cable TV coax back to the grounding block, plus the piece of wire from there to the actual ground.
In reply to:
The addition of the 500, with its sophistication, either picked up the hum or helped creat the loop.
It was probably the latter. You didn't by chance happen to plug the sub into an outlet on a different circuit than the reciever and/or TV, did you?
I'm glad it all worked out. I think the cable guy should have fixed it for you. If you know any electricians in the area, ask them what the code is for cable TV grounding. In my county, they are required to ground to the same ground as the electrical panel. If they don't, they are breaking the law. It is a "safety" issue. If they try to bill you, let them know that you heve decided not to notify the public utilities commission, but would appreciate some credit on your account to compensate you for properly grounding their connection.
If you don't know any electricians, drive by some of the gentlemen's clubs around 4:30 on any weekday, and look for the company vans in the parking lot. They wear names on their shirts, so they're easy to find once you are inside. I'll bet you can get your answer for the price of a highly overinflated beer.
