I occasionally have folks ask me, "Why does my computer make that noise?" I usually tell them it's nothing more than the hard drive doing its thing as the computer boots up. Hitachi, a maker of hard drives that are in many computers, has a page that contains sounds that their hard drives make if there are various problems. I personally have not heard any of these sounds, because the computers I have worked on sometimes use IBM, Maxtor, and Western Digital hard disks. They don't have quite the same sounds. Anyway, I thought you might find it interesting.
Hitachi defective hard drive sounds
Saw this on Digg. Interesting and cool video of how a hard drive works. Now you can see what it actually looks like on the inside as well as how it works. This is part of a Colorado State University Controls Lab demonstration.