Several recent reports surrounding a number of issues with Apple's top-of-the-line desktop computer, the Mac Pro, suggest the gang in Cupertino are acknowledging the problem and working on solutions. Some Mac Pros with the Nehalem processors have been experiencing high CPU usage and poor performance during audio playback. These issues are made worse by the processing not being recorded in Activity Monitor and thus not activating necessary fan operation to reduce heat.
An article states:
The problem is most glaringly illustrated by merely playing music using iTunes. Though Activity Monitor will report just 1 to 3 percent CPU load, CPU power draw will increase tenfold and CPU temperatures will hover near the safe limits reported by Intel with little or no fan activity. Users were also able to reliably demonstrate a 20 percent decrease in performance, even with something as simple as plugging in FireWire- or USB-based audio interfaces.
A workaround found by some users requires using a PCIe audio card instead of the standard, onboard sound card. Several users have reported that Apple technicians are both aware of the issue and working on a solution. I imagine we will see a permanent fix when Mac OS X 10.6.3 is released.
The OS upgrade is currently making its rounds through beta testing and should be available shortly.