Hi,
I updated my graphics driver late last year and ever since then the fans on my GTX770 seem to speed up slightly now and then, changing the tone and generally being annoying.
It finally annoyed me enough to search for others with the issue and found a thread on the Geforce forums:
This sounded exactly the same issue, so I rolled back to the 344.11 drivers and lo and behold, the noise stopped!
The fix for MSI card users, to allow updated drivers to be used and remain sane, was to get a bios update. Is there such a thing available for my EVGA card? I could not see anything via the product support page, but I can't be the only one who has been driven to distraction by it.