Received Refurb G5 - Fans Are Full On

[N-OS X-tasy!]

This behavior is typical of a machine which requires thermal recalibration of the processors. The G5 processor must undergo thermal recalibration whenever it is removed from and added back to the motherboard; it's a good bet your machine didn't undergo the recalibration process before leaving the factory. The same thing happened to one client of mine; my local Apple house had it fixed in less than an hour.