Hi Skimble,
Hum problems and "ground loops" are really annoying, but all of them can be solved. In addition to that link to my article on hum problems, here are some updates and links to two inexpensive ground-lift transformers, either of which, depending on the source of your ground loop, will solve the problem.
Cable systems are seldom at "zero ground potential", which means you'll get ground-loop hum when you integrate any audio-video gear with a cable-TV feed.
Try one of these video ground isolators and install it in-line with the cable before it enters your set-top cable box:
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=180-075
Did you try disconnecting your subwoofer from the coaxial cable connecting it to your JVC receiver? If so, did the hum go away? If it did, you could try one of these from Radio Shack, which goes between the subwoofer and the coaxial cable from your JVC a/v receiver
http://www.radioshack.com/search/index.jsp?kwCatId=&kw=ground%20isolator
&kw=Ground+isolator
I would first try the in-line video ground isolator from Parts Express.
Regards,
