Still no dice. I unplugged my external HDD before shutting down and the fan stays on. Actually, I can flip the PSU switch off and back on, turning off the fan, but hours later, I can walk back in the room and the fan will be turned on again. I had my portable HDD (WD Passport) plugged in when the computer went to sleep and that even stayed on, so the USB ports are powered even when the computer is off. Maybe my mobo stays on kind of like how yours is Bunni, but the PSU keeps a fan on because of this action by my mobo?

Im at my wit's end here. Any suggestions?