I've had run into this problem after owning my 760 for 2 months. (Owned it for about 8 now)
https://www.youtube.com/watch?v=chGO47cfy1k (Heaven Benchmark to showcase the problem) Seems like some sort of graphical glitching/artifacting/whatever you want to call it. I contacted Nvidia about the problem a while ago, but they couldn't find out what the problem was, so they suggested I sent it out to Gigabyte to be replaced. I haven't done that yet because of school, and I don't have a replacement card for the 2-3 weeks my card will be gone. Last week, a guy at a computer store mentioned to me that it's probably because the card has 'bad video memory.' Does that seem right? I'm assuming that's gotta be the case, because I cannot think of any other reason why the card is performing like this.