My brother's PC has been causing PSUs to spin their fan loudly at 100%. Any PSU, including my Cooler Master Silent Pro M 600 (40A on the +12v rail) will spin to the maximum when plugged in to the motherboard.
We determined that this was likely caused by the motherboard which he had previously shorted by forgetting to put in the spacers. However, we ordered a new one of the exact same model and when he put it in (without shorting it) the same thing happened. Almost.
Now instead of a constant 100% spin, it starts at 100% for about 3 secs then pauses then resumes 100% indefinitely.
His PSU works in my PC silently, and as I said my PSU spins up to 100% in his. And even if the motherboard and CPU are the only things plugged into the PSU, it still spins 100%.
Which leaves only 3 possibilities. (I think)
The new mobo is defective
The CPU fan has a sick sense of humor (and evil spirits)
The CPU has a weird voltage issue