I solved my ground loop hum coming from cable box by installing the isolator from Parts Express several months ago. It was suggested by gonk and it works great. No more noise from the speakers.

I installed the ground loop isolator from Parts Express as well. It's made by Dayton. The "buzz" is gone however, I have a problem with my HD signal when the isolator is installed. It degrades the signal enough that I lose a couple of HD channels and a couple of others break up. I originally thought this might just have been a bad night for the cable company as we have had a lot of windy weather here, but as soon as I took the isolator out of the system the picture was fine. I may have to try the more expensive Jensen Tranformer piece to see if that keeps from degrading the video signal. The Dayton part did get rid of the "buzz" but I obviously don't want to lose video quality as a result.

I used the Jensen to eliminate the ground loop caused by my cable. I have HD service and there was no loss of video quality with the Jensen.

It sounds like you are on the edge of not having a strong enough signal at your box. I've had numerous problems with that at our current house, mainly affecting the cable modem. The best bet is to contact your cable company and get them to either fix whatever is causing the drop in signal quality or add a booster at the box.