OK, I also did some tests now. I wasn't patient enogh to do it for an extended period of time, but long enough to be able to confirm the theorie you developed during the course of this thread.
In idle state with my USB audio interface unplugged my temps were at 31°/27° C for CPU 1/2, ambient at 22°. Power was at -0,75W/-0,5W (?).
I played music in iTunes until the temperatures stopped rising, which took about 10 minutes (I can also confirm that even the blip sound when pressing the volume keys causes the temperatures to rise). They rose to 52°/42° at 21,88W/22,88W. As soon as I stopped playback the Power values fell slightly below zero again. Ambient temperatures rose to 25°, which is probably due to bad heat dissipation caused by my Mac Pro standing pretty close to a wall corner.
I let it cool down to about 30° again and then plugged in my USB interface (Tascam US-122), which made the Power values immediately jump to 22W/25,88W and the temperatures start to rise.
So, I can confirm the problem with audio interfaces, and I also feel sad now![]()
Do you own a Octo? Because 22W seems very low
Idle for my 2.66Ghz Quad is around 10W and this bug makes it 50W and 1080p HD encoding load is 6x W.
Also interesting finding about the FW800 HDs... I shall try that one (although with only one FW800 disk) soon!
This also explains why a USB webcam w/o audio has the same effect.
Oh deary deary me...
This seems like quite a MASSIVE bug and it seems it must be deeper than CoreAudio if FW disks and USB webcams make it do it, drivers/kexts?