I get that from time to time. I'm running 2 x GTX 670 in SLI. It's happened to me in Far Cry 3 at highest resolutions, World of Tanks, Planet Side 2, and even Dragon Age. Usually my computer freezes for a time and graphics cards sound like afterburners. There's no rhyme or reason when it starts. I wonder if there is some conflict between the Precision X software I use to OC and the drivers. I've noticed that the fans are still ramped up but the temps are normal.
Usually I hard reboot and everything goes back to normal.