Initially it was only 2 or 3 white horizontal lines started to appear on top of my TV screen. Time to time, not always on the same channel either. But now, the lines are start to creep further down. I was told by Rogers that it's either the cable box or the TV. Since it's free to replace the box, I did that first. Unfortunately, it wasn't the culprit. I guess I have no choice but to replace my TV.
The issue you described does unfortunately point towards the TV. Have you check your cables? If you're using an HDMI cable, try replacing that to see if it fixes the issue. I've had this happen on my old plasma once except I had vertical green lines across the TV. It ended up being the flex cables inside the TV that connect to the board.
You could also try a different input point for the tv as well. If you are using an HDMI cable, try an RGB cable set if you happen to have one available, or composite video cable. That might show that the problem is with a specific input for the tv, and not necessarily the tv as a whole. That might not totally help, but might point out that the tv isn't necessarily a write-off.