This first occurred with DIY, I changed the channel, came back to DIY, was fine for 30 minutes then it occured again. The whole time the audio was normal.
Did the soft reboot and changed the channel to TNTHD thinking it was the channel and about an hour into watching the channel, it started again, again audio was fine. So I unplugged the receiver and ate dinner.
Came back plugged it in, went through normal startup from being unplugged and flipped on HDNet while I was finishing cleaning up from dinner. Sat down and video was all jerky again, but audio fine. Flipped channels, came back and it was normal.
OTA channels are all normal, only get the occasional problem I have always had where audio drops now and then for a second.
Another note as this is my second 811, I did get a replacement due to a short out in my original.