I really don't know what the problem is. The line appears on all channels of all inputs. Cable, Xbox 360, you name it, it's there. Turned the TV off one night, woke up the next morning and turned it on and there it was. RCA wants me to send it in, Walmart won't print me out a copy of my receipt without a police report or court order. I've gone through all the picture settings on both the cable box and TV with no results.
Here's a pic of what it looks like: