The very first thing I would do is to make sure my data is backed up. Frankly the crackers thing sounds like a fan. I'd hook it up in Target mode using a firewire cable attached to another Mac. Hold the "T" key down on the G$. Your hard drive icon should show up on the desktop of the other Mac. You can now run Disk Utilities on the hard drive. See if you get the noise when the hard drive is active. I've seen fans on older macs start to come off. They are pressed onto a center hub and yuou can pull them off. This is just speculation on your machine. You can tell by pressing them in with your fingers, if they move you can glue them back into place.