If you are using a surge protector/line conditioner with a 3 prong cord, lift the grounds on all of your other components that use a 3 prong cord that happen to be connected to the surge/line unit. If you have already done this and the problem is still there, you may still have ground loop problems from your cable/Sat. provider. There are devices you can use that will eliminate that problem. Radio Shack sells them, or you can go to your local Home Theater dealer and possibly pay through the nose for the same sort of device in a fancy jacket. Tributaries makes a pretty good one that is not too expensive.
Good Luck
Good Luck