This may have been covered, but when I moved into my new HT room, my HD DVR had constant pixelation and frozen screens, while it was generally fine in the previous room. I added a drop-amp in the line in the attic and had the company run a new line to cut the cable run to this location by 2/3 and no more problems. For me, it was just a weak signal. A friend had a similar issue house wide. We added an amp and the problem cleared up.
Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire