Gah, just found out that one of my fans appears to have gone south. Not sure when that happened, but it apparently has been lying to the motherboard, saying that it's doing the fan thing (y'know, spinning and such) while not doing any "rotations per minute" at all.
Funny enough, when I unplugged the one fan, it appears that the other fan didn't feel like it needed to overcompensate for the other one. Machine is as quiet as ever. Hopefully it won't overheat until I can get a new fan.
(just for the record, it was an Enermax fan; one of those fans that apparently has the lovely blue LEDs on it that thankfully has a switch to turn the blue LED-ness off. Unfortunately the one that was covering for it is an Antec, which has fan speed control, but no discernable way to turn off the blue LEDs off. And folks wonder why PCs get the bad rap in the design arena.)