I've had this problem before and I somehow fixed it about a year ago but now it is back. My CPU fan is stuck at 100% and is loud and rattles. The cooler and fan I have is a Cooler Master 212, the fan is a 4 pin and it rattled right out of the box but only at full speed. I've tried Speedfan, it works but it resets each time I turn on my computer. It used be controlled automatically and stay silent each time I turned on the computer. This happened today as I was putting spare ram from another computer in mine to test performance differences and when I went to take the memory out I somehow got to the screen to either Start in Windows Recovery (recommended) or Start windows normally. I chose to start windows recovery, because it recommended it, and then the fan cranked up to full speed. It is getting frustrating that I can hear the fan rattle from two rooms away and I can't find a way in the BIOS to change auto fan speed, only target CPU temperature.