Horizontal Banding on RPTV

Recently I've noticed, in this case while playing SSB: Brawl, that there are horizontal bands, maybe an inch apart from each other, that appear in dark sections of the screen - most easily seen in greys. They appear to travel down the screen somewhat quickly. Lowering the brightness doesn't help -- they are still prevalent.

I haven't tried with other inputs, but this is with a Nintendo Wii connected with component cables (third-party) running in 480p on a 47X54 Panasonic RPTV. Are the cables to blame? Or is there some sort of interference?

How do I fix a ground loop?

Maybe this will help:

I have the TV plugged into one outlet - it's a 3-prong plug. I have a power strip plugged into the same outlet, with a receiver, DVD player, Wii and 360 getting power from that. The subwoofer is plugged into a separate outlet. The cable comes from the wall, but there is a connection between two separate cables. I thought that might be the problem, but disconnecting the cable doesn't change anything.

Anyone know anything about ground loops?