[Cory Bauer]

I've got a revision A Dual 2Ghz Powermac G5. The machine has started to emit what I can only describe as the sound of grinding glass from the hard drive bay area. The machine appears to be running fine otherwise, which leads me to believe it's not the hard drive itself, but something else in that area (a fan perhaps). Anyhow, it sounds awful, and I'm unsure what to do about it. It's only happens occasionally, but it seems to be happening more frequently. Any thoughts would be appreciated. Thanks!

[Dzokayi]

Media bay fan would be my first guess... Check disk utility and make sure the SMART status isn't indicating an imminent drive failure

If it is the fan, and your box is under warranty, Apple will replace the entire enclosure.

[Big Mac]

I agree - run AHT.

His G5 wouldn't be under warranty because he said it's a Rev A. My Rev B's AppleCare just expired.

[Waragainstsleep]

Hard drives can make noises while displaying no other sign of malfunction. Backup whatever is on it.
I would say get another one and clone the first one onto it. Then you can disconnect one at a time and see if the noise persists. If it does, its the fan, if its the fan, well theres no harm in having more storage.
If you already have two drives, you could try disconnecting one by one and using target mode (disk probably won't spin up for long if it has no boot volume). Its whether or not you can hear the glass noise over the rest of the fans running full blast.

[chris v]

It'd be really easy to tell if it was the fan in the HD bay. Pull the aluminum cover off, and jently jam a pencil eraser into the fan just long enough for it to stop spinning.