I had the same problem with my Directv box and EP500. I moved the sub a little further away from the STB and the problem went away. I don't think it was a vibration problem as much as an electrical interference problem. I think it had to do with the way the cables ran along side each other. It was a strange effect on the screen, kind of what you would expect if you laid your head on the subwoofer while you were watching TV. The bass would "blur" your vision.

Don't get caught dead with a necropyliac.