This is a very common problem. Maybe your cable company will fix the issue, however thay may blow you off too. There have been many post regarding the subject here on AudiogoN (search the archives). All you need to do is isolate the incoming coax from your system usng any one of the many isolation blocks. You can spend nearly $100 on the Mondial Magic Brick or you can get a comparable Jensen or Radio Shack unit for a lot less money.
Enjoy,
TIC
Enjoy,
TIC