i wrote about this same issue in another post. one of the "techs" on this forum suggested installing a terminator on all unused coax branches and/or splitters, to try and cut down on signal distortions. i haven't done it yet, as i can't find any store in manhattan who sells this item, so i'll have to order it online.
Have had FIOS DVR for a couple weeks now. Among the issues I've seen so far, the other day the picture suddenly wigged out, showing a rolling warped video. Initially thought the TV had crapped out, then examined cables after confirming the TV fine using DVD as baseline, finally turned off and pulled the power cord out of the FIOS DVR for 10 seconds then powered back up.
Problem was gone.