Ok, I've just been sitting here playing a flash game for about a half hour and my GPU fan just revved up for less than half a second and went back to normal, totally out of the blue. It sounded like someone revving the engine on a car really quickly.
Afterburner and speedfan weren't running and my clocks and voltages are set back to defaults.
I opened afterburner immediately after it did this and my GPU was only at 53C. There is no reason for the fan to ramp up if the temps are not increasing.