here is the setup, 2 rooms, both have hd comcast boxes hooked up through component cables to plasma tvs.
one of the tvs has artifacts on 3 channels, 804, 805, 807 all the other channels are fine. the second room has no artifacts on the same channels. until 4 days ago both cable boxes were fine, no artifacts.
I went to the comcast office and swapped what I thought was a bad box, same ****.