I too have been having picture quality issues as well. It is not just one channel but various channels. Seems like it is worse on the sports channels. The issue was so bad a few weeks ago I had to shut the hockey game I was watching because it was giving me a headache watching the scrambled picture. The only issue I had with the audio was the picture and audio did not sync due to the pixilation issue.
Does it happen on all boxes?
Have you tried checking coax connections?
Start at ont and check all connections for tightness?