Ground loop when connecting coax to cable box.....

Ok here is my issue: I recently got my home theater set up and as soon as I physically connect the coax cable to my cable box I get this mad ground loop noise coming through my system speakers. I have ran into this in the past with this system when I plugged the amplifier into it’s own circuit and the processor into a different circuit. So to correct that issue I installed a high amperage dedicated circuit for all my home theater equipment. This completely resolved the ground loop feedback noise issue. However recently I bought cable and if I have the cable box connected in anyway to my sound processor and then connect the RG 6 coax cable I get the ground loop noise. Even if the cable box is not plugged into a power outlet I still get the feedback noise. So to explain a little further as I am not sure if I’m being clear, I basically have the audio RCA’s plugged from the cable box to the sound processor and the RG 6 coax cable to the cable box I get the noise. Same deal if I have the DVI cable hooked up from the projector to the cable box with the coax hooked up. Does anyone know how cable is supposed to be grounded? I would have thought (NOT an electrician here so be easy if I am way off here) that it would get grounded when you connected it to the cable box through the ground plug on the power cable? Or does this get grounded before it gets to the cable box for example on it’s own earth ground? If so how can I get this to work without the ground loop? Any advice is greatly appreciated!!

Mello