This link should come as quite the resource for any nerd who has wonder WTF that noise is coming from their harddrive and why it might not be working anymore.
Canadian data recovery company, Data Cent have a list of numerous failing harddrives, a sound bite and what is causing the failure.
I for one have heard far too many of those noises in my time and can now finally know if its me or if the drive is actually failing…. YAY!