I've been noticing periodic extremely loud fan noise while gaming for a while and decided to track down the issue tonight. For some reason my card won't spin the fan if its set to less than 87% max speed. It was set on auto, and would passively cool as long as it was below about 80-82c, then would spin the fan up at 100% until temps dropped below 80, which caused the fan to stop again. Under any load this means the fan is constantly toggling between 100% and 0.
My card is a radeon 7850 running windows 8.1x64 on my desktop. I hadn't updated my drivers in a while, so I tried that first with no change in fan problems. currently v17.4.4 installed.
Here is side by side screenshots with the fan speed manually set. Note that the fan isn't moving at all when HWmonitor reports 251rpm. The card wasn't under load when the shots were taken, but it performs identically when the speed is set manually under load, it just gets hot really fast if set to less than 87% since the fan isn't running at all. There is no sign of physical damage to the card, and the fan spins without resistance. It seems to work fine at high speed too, it just refuses to spin except at very high speeds.