HD CRT with scrolling feint lines

I have a 27" magnavox HDTV that has been driving me crazy. There are very feint lines are most visible on HD content that is mainly white. I am unsure whether they scroll the entire picture, but they are always the most visible in two spots...near the top third and bottom third of the picture. I took my tv into a repair center, and they looked it over and called me back telling me that their HD signal generator was putting a perfect image through the tv with no lines like I had mentioned. When I got it back I assumed it must be a ground loop or cable problem. But when unplugging the cable from the wall outlet did not solve the problem, I became frustrated and tried removing every piece from my set up. I have the tv, an onkyo 7.1 channel speaker, 7 speakers, powered sub, hd dvr, a cable modem, and an xbox 360 all in the room. When I tried to isolate the problem I was unable to find any individual piece that was causing the interference. I would LOVE any help or suggestions to try because I am at the end of my rope with this. Thanks in advance

Are they dark and are they a hair line? And don't move

they are kinda see through, they dont prevent me from seeing the image since they are the same color as the picture. I suppose when its on a white background they are kinda dark , somewhat hard to describe. And they definitely move some, at least 3-4 inches, if not the entire screen...just hard to tell sometimes since I always seem to notice them in the same areas. Does that help any?