If you are connected to a coax cable TV feed, it is likely that the cable is causing the issue. This is VERY common and has been widely acknowledged on this and other forums. You can purchase an in line isolation unit that will solve this issue. I know there is one made by Mondial and I have read that Radio Shack sells a similar unit. I think the Mondial sells for about $99 new. Here's a link to an A-goN ad for a used one. BTW, I'm not associated with the seller.
http://cgi.audiogon.com/cgi-bin/cl.pl?accstwek&1060908005
I hope this helps.
TIC
http://cgi.audiogon.com/cgi-bin/cl.pl?accstwek&1060908005
I hope this helps.
TIC