I've been having a similar issue recently. The black line across the screen plus bad pixelation would actually carry from channel to channel for me. So if I was watching BBC HD and this started to happen, when I changed channel it'd be happening there too. Has your box begun rebooting at inconvenient times, especially when recording and watching HD channels at the same time? If so you may have the same problem I've just had fixed:
http://www.cableforum.co.uk/board/11...ast-night.html