Overzealous fan in my Mini


Crotchety UI Nitpicker
I've had my Mac Mini for several months now. I've been very impressed with the fact that it's silent most of the time; I upgraded from a fanless iMac DV+, and I was not looking forward to having to hear a fan all the time. But it turned out the Mini's fan was almost always idle, so I was thrilled.

But for the past week or so, my fan has been whirring (slightly) almost constantly. I check Activity Monitor, and nothing unusual is happening. I have no idea why the fan thinks it should be going.

It's not a huge deal — the fan seems to be on its lowest setting, which is definitely quiet enough to accept (quieter than my old fanless iMac, even, because it had a whiny HD). Still, I think something must be wrong, and I would love to get my silence back.

Any ideas what might be causing this or how to fix it? I already ran the Apple Hardware Test, and everything passed (I also heard the part where it tested the fan, and it sounded the same as the last time I ran it).

I'm not sure exactly, but I guess it started around the same time I applied the 10.4.2 update.
Since owning my powerbook, each update seems to mess with the cooling.
10.3.7 ran cool, 10.3.8 ran hot, 10.3.9 ran very cool, 10.4 ran hot, 10.4.1 ran very hot, 10.4.2 runs cool.
Since my software installed remains the same (mostly,) throughout, I can only assume that it is the updates that make the difference. I don't have a solution, just my observations.