Just as a test, disconnect the main cable service from the distribution system and TEMPORARILY disconnect the cable ground where it enters the house. If the noise disappears, you have a grounding problem.
Pick yourself up a coax ground-loop transformer and install it on the main cable service before it enters the distribution center.
These are available from www.partsexpress.com
If you can't find one. You could hop down to your local Radio Shack and pick up two 75-300 ohm antenna transformers, wire them back to back, and install inline like described above.
Hope this helps.
JJPThis message was edited by John Pechulis on 01/26/02 19:14.09.