Late-2013 Mac Pros have two hardware issues that have been fixed in a recent Mac Pro SMC Firmware update. The first is that when you hold down keys at startup, they will be recognized after updating the firmware (previously it was hit or miss if the key was detected at boot). The second is if you put the Mac Pro into Power Nap mode, it no longer runs the fan that is located at the top of the unit after updating the firmware, thus keeping the Mac Pro completely silent.