I have recently bought a GTX 560 Ti and I have noticed strange translucent "lines" like an old TV. (The strange lines doesn't appear in screenshots)
This mostly happens while playing a game but very notice-able in S.T.A.L.K.E.R., although it doesn't happen in APB:Reloaded and only happens a little bit in ArmA 2's main menu screen, in-game, it's gone.
My system specs are: (Hopefully upgrading to a much more powerful Sandy Bridge soon, but I'm waiting for Zambezi FX to be able to choose between them)
one possible scenario is that your card is running too hot during gaming. when the gpu's get too hot, you will see something called "artifacts" on the screen which can be lines and other weird screen anomalies that pop up. if this is the case, then turn up your gpu fan speed when you are gaming, which will drive the temps down and you will no longer see artifacts.
Hmm, yea 60C is great temps for load during games. Try installing the latest drivers for your card and see if it goes away. Also try going on the Zotac forums and see if anyone else is having your prob. If not, then I would probably return the card for a replacement.
It could be due to the fact that the card you've got is damaged. You should send it back to get it repaired.
When did you buy the card ?
Did the card showed this sorts of stress when you bought the card at first ?