ARS Technica reports late-2009 Nehalem-based Mac Pro systems suffer from a weird power management issue that increases the CPU temperature by 30°C or more, along with performance decreases of up to 20 percent. The problem occurs when playing songs in iTunes, watching videos via QuickTime, or even when keeping USB or FireWire audio devices plugged in.
It turns out that the most recent revision of the Mac Pro—"Late 2009" models—exhibit very unusual behavior when playing any source of audio. The problem manifests as what has been described as excessive increases in power use and processor core heat when playing songs in iTunes, watching videos via Quicktime, or even when keeping USB or FireWire-based audio interfaces plugged in and active. While hardware monitors only report a small percentage of processor use, it can still cause performance decreases of up to 20 percent for other tasks.
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.