It may be your video card / drivers.
Reason: My brother recently bought a ViewSonic VA720 LCD screen. I have the exact same one. We also have the exact same video card 4200Ti.
On his machine, there are occasional lines that move from bottom-to-top. Light gray ones. I thought it was his refresh rate. Nope didn't work. Updated his drivers, nope didn't work. His LCD was right next to a speaker, moved that, nope didn't work.
I thought that it might be a bad ViewSonic, but as soon as I hooked it up to my machine, it was perfectly fine.
My conclusion is that the monitor is in good condition, but something in my brothers system is creating those lines. Perhaps a reformat would help. Perhaps its the powersupply?
I recommend you try the monitor in another comp/video, like Mscrip mentioned and pinpoint the problem. The lines however died down for my brother, he doesn't see them all the time now and are very thin and faded. I'm still puzzled.
danny~!