If you have a new Mac Pro, check Software Update for Mac Pro SMC Firmware Update 2.0, a change to the System Management Controller (SMC) firmware used in your shiny new computer.
According to Apple, the new SMC 2.0 update "enables the Mac Pro to enter Power Nap without running the fan for most Power Nap activities, and addresses a rare issue where a low-speed USB device may not be detected at boot."
Power Nap is a feature Apple first introduced in Mountain Lion, or OS X 10.8. It enables your Mac to establish a network connection even when it goes to sleep, so you can receive new mail messages, sync content through iCloud, download software updates and more.
The System Management Controller is the part of your Mac that is responsible for, among other things, power management, waking it from sleep, thermal management and more.
If you have a new Mac Pro and you run the update, let me know if you notice a difference!
Thanks Marc Edwards!