brand new Mac Pro tower fan suddenly runs full-tilt, CPU is idle

My Quad-Core MacPro tower is two days old. Initially, I was impressed with how quiet it was compared to my older Macbook Pro. Then on day two, for some reason it started running very loudly. It's not just a "little" loud- my wife walked into the room and asked what the noise was.

At first I thought this was just because I was hitting the CPU a bit (importing my iPhone library into iLife '09, and running Eclipse). But I tried powering it off & letting it cool down for a few minutes to no avail; about 10 seconds after powering up, the box gets loud again. I took a look at it with the side cover off, and it seems to be the fan near the top middle, between the power supply and the disk drive.

It can't be a dust issue, as the machine is only 2 days old (and I peeked inside anyway just to be sure- clean). I did do a software update over the past 24 hours or so, but I can't say that it occurred immediately after that. I also did a migration of my old apps and data from my MBPro, for what it's worth.

Why is it suddenly so loud? How can I monitor the fan speed and various system temperatures?

Thanks

EDIT: Activity Monitor shows a virtually idle CPU; there's nothing running that ought to be causing this, as far as I can tell.

Here are my temps: http://imgur.com/J6BLf.png

Message was edited by: armhold