Results vary somewhat, but several users told Ars that processors that typically measure about 30°C while mostly idling will rise up to 60°C or higher when doing anything that relies on the audio subsystem. Additionally, the amount of power used by the CPU increases significantly.

"When idling, the CPU power draw reported by iStatMenus is around 4 to 5 watts," Ceri Haddon, who owns a brand new, 2.93GHz quad-core Mac Pro that was produced in January, told Ars. "Opening iTunes and playing an MP3 file instantly increases the draw to over 50 watts, whilst the reported CPU load remains down in the 2 to 3 percent region, as expected."

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Users in Mac Forums and Apple Discussions have performed numerous tests that show the issue is real, only affects late-2009 Nehalem-based Mac Pros, and only shows itself under Mac OS X. Previous Mac Pros do not exhibit the same symptoms, nor do MacBook Pros. Strangely, booting affected Mac Pros into Windows 7 also eliminates the problems, leading one user to suspect the issue is related to power management kernel extensions. Additional tests show that the problem happens even when FireWire or USB audio interfaces are plugged, even if they aren't actively being used.