|The only time I have heard a really high pitched sound like that, it turned out it came from a dying Maxtor 80gb hard drive on a friend's computer.|
It wasn't long after that the drive could not be accessed at all - a day or two.
Check your hard drive with the manufacturer's diagnostics.
See the latter part of response 1 in this:
(thanks to Dan Penny for this link:)
Hard Drive Diagnostics Tools and Utilities
If you don't have a floppy drive, you can get a CD image diagnostic utility from most hard drive manufacturer's web sites, but obviously you would need to make a burned CD, preferably a CD-R for best compatibilty, on another computer if you need to.