Yeah that's either artifacting due to heat. Or you have model problems, and if you delete your local game content in Steam and redownload/install, you should be okay.
If it's the heat thing, check the heat of the card (Google SpeedFan, it'll tell you), and if it's running very high, try to underclock it (Google Overclocking and do the opposite). If that doesn't do anything, your card may have faulty cooling, and I would try to get an RMA or similar.