Call up Comcast and see what they have to say. OTOH, I've had to swap boxes several times (because of mostly DVR issues) before I got one that stuck ;).
I have the pn58550 and have had it for about a month. I have noticed on a couple channels especially fox or local hd tv that there seems to be this distortion in the picture. the best way I can describe it is when i used to play a scratched or dirty dvd and the picture would get these small squares that would pop up and move around erratically until the picture would freeze or get bad enough were you can not see the picture at all. basically what is it and is it the tv or cable? it is only on a few stations and have had no problems with my samsung 3600 while playing blue rays. i have a comcast hd cable box. thanks