Originally posted by jamil5454:
Sounds like a slight vibration problem or a bad bearing. The vibrating problem is more common with PCs, but can happen on any machine with movable parts. If you feel like voiding your warranty you could take apart the PSU and replace the fan yourself. It would be a fun project. Or you could take it to a shop and they'd probably replace the fan for you.
Ignore the PC user that knows nothing about G5s. The G5 power supplies chirp. I've never heard one that makes loud noises, but I've also never heard one that doesn't make noises. My best guess is that it's coming from capacitors inside the machine.
BTW, DO NOT TAKE APART THE POWER SUPPLY. If you take your machine in for service, they also will not be taking apart the power supply. The whole thing would be replaced.
If the machine is under warranty, you can talk to them about letting them diagnose the problem, and then you can use the machine until the part gets there. If they have a backlog of machines to work on, you can get your name in line.