Here is a great page. It has 6 sounds that hard drives make. Do note that these are sounds you also hope that your hard drive isn’t making.
I have heard a couple of these coming out of my case before actually, fortunately knew enough to know that was an indication to start backing up whatever I didn’t have already on a different drive or dvd.
Over at PC Tech Guide, you can learn a little bit more about hard drive construction if you are curios. Knowing the parts of the hard drive, and those sounds, can help you diagnose problems if they creep up on you. Possibly saving yourself time, effort, and money.