vertical bars on television

I've got a 25" RCA television. When I have a video component (receiver or just the dvd player alone) plugged into the composite video input, and the cable TV wire plugged into the television, there are thin (abount 3/4" thick) vertical bars that scroll from right to left. They go away if I unplug the cable-TV wire, and they don't show up at all when i'm not watching something through the video input. There is no audible hum through the speakers (like i've had with previous ground loops), and none of the components (television, receiver, VCR, DVD) have 3-prong connectors.

Are these "hum bars", or something different?

Any help is greatly appreciated.

Jeremy Volkman