TiVo HD Issue: Flashing / wavy picture

I hate to post a new thread, but I've read through most of what is here and did not see my issue discussed:

I have a TivoHD with 2 Motorola S-Cards. When watching live or recorded content, I will get a "wavy lines" through the screen typically near the bottom that clear up after a few seconds.

Also when changing scenes within the same program/channel (not changing the channel) the screen will "flash" or "flicker". This happens more when there is a bright background but does happen in all shows/channels.

These issues occur on all channels, live TV and recorded programs. It does not appear to be The Comcast DVR that was just removed operated flawlessly with the same cabling and connection.

I do not believe these issues are the same as the pixelization/macroblocking discussed here because the symptoms are not the same.

My TV supports 1080i, 480i, 480p.

Are there any settings / troubleshooting that can resolve these issues? It happens several times per minute in some cases making the TiVoHD useless.

I'd hate to go back to the Comcast DVR, but it had a flawless picture on the same connection/equipment.

Any help would be greatly appreciated.