Firewire audio interface causes high fanspeed

Whenever I plug in a Firewire audio interface, even with no programs running and the computer essentially at idle, the CPU temperature quickly rises several degrees and then the fan quickly ramps up to maximum. Nothing appears to be placing the CPU under load at this time (measuring temps and fans with iStat nano). So, for instance, my CPU temp will be at about 60C, and I'll plug in my
Apogee Duet, and the temperature quickly rises to about 68C. The fanspeed follows, rising to maximum and staying there for as long as I have the Duet connected. This happens with both an Apogee Duet and a Presonus Firebox, so I'm pretty sure it's some issue with my mac. I usually run my macbook in clamshell mode but it happens with the case open also.

Here are the specs of my macbook:
late 2006; core 2 duo 2 ghz
running leopard with all updates applied
3 gb ram
320 gb hard drive
wireless apple keyboard / wireless mighty mouse

I found a thread on macrumors where someone had a very similar problem but no resolution was ever posted (thread is here: http://forums.macrumors.com/showthread.php?t=314270 ).

Can anyone recommend steps I can try to resolve this? Or point me in the direction of the cause of the problem? I'd love to keep my new Duet but if I can't resolve this I'll probably have to return it.