Awful squealing, then unresponsive?

My iBook woke myself and my 2 hotel roomies on vacation up last night at 5:30 a.m. squealing and squeaking quite loudly when it was supposed to be asleep...the processor area was warm (but not as warm as it has been in the past when doing processor intensive activities) and the noise seemed to be emanating from the fan. The computer was completely unresponsive, so to stop the noise in my sleepy state I pressed and held the power button, powered it off, and went back to bed. When I woke up in the morning it couldn't find the startup volume. I zapped the PRAM because it was the only thing I could think of to do in the hotel this morning, and that didn't help (figured it wouldn't but it was worth a shot).

So later today at home I booted from the install disc, thinking the hard drive had gone bad, ready to try anything I could to repair the disk or at least be able to retrieve some files from it (not that there's much on it, it's not my primary machine). I ran the disk check on the hard drive while booted from the CD, and it found no problems. Baffled, I ran repair anyway and it said it had nothing to repair. I also repaired the permissions just for the heck of it. Told it where the startup volume was, and it booted fine from the hard drive. It ran for approximately an hour before it started making the same godawful noise again and was once again unresponsive...wouldn't sleep, couldn't click anything, and a couple of minutes later the display shut down but the noise continued. I had to power it off by holding down the power button, and once again it cannot find the startup volume.

I'm not exactly sure what to do or what on earth is making this noise...the hard drive is fine, there were no issues during the disk check, I was able to burn a CD with my Documents folder on it and a few programs I want to save, and it doesn't seem to be hot because I wasn't doing anything with it...I was using the iMac and the iBook was sitting alone on a TV tray across the room, untouched. I hadn't used it for about 30 minutes before it started making that noise. Last night, the elapsed time between last use and the noise was about 5 hours. It seems to be emanating from the lower left, by the vents, which is what made us think it was the fan...but now I'm not sure. Tilting the computer or moving it in any way doesn't make the noise stop either. I'm completely baffled. Any ideas?

(Naturally, this would happen 5 months after the AppleCare I paid for and never used expires.)

Unfortunately I can't monitor the temp with the widget because now it won't boot from anything except the CD... It can't even find the hard drive now to check it with the disk utility, which is odd since just an hour before it said there were no problems and nothing to fix. So now I'm really confused...and it's going to the Genius Bar at noon today to be checked out. If it is the hard drive, though, I'm just not sure I want to sink $300 in repairs into a 3.5 year old computer (nor am I brave enough to try the repair myself since I need some sort of laptop for school and if I screw it up I'll really be screwed because then Apple probably won't take it... *sigh*).

Took it to the Apple store, got it checked out by a genius...the hard drive has gone bye-bye and it would be $300 to replace. So I bought a "refreshed" (i.e. returned) Macbook for $899, not a mark on it...I think I got an awesome deal there. The staffer who actually completed my sale was rude to me which was disappointing especially since I have always had good experiences there and felt very welcome even when I wasn't buying anything. The genius and the manager were both great though. I plan to file a claim with TSA since I suspect the hard drive failure is related to the strong jolt it received upon being shot out of the x-ray machine at the Columbus airport last week. If they'll pay for the repair then I guess my fiance and I will start married life with two laptops.