Here's a site which let's you hear those sounds you never want to hear from your own drive
Well the link seems to have an error on it now.
Will wait a bit, and if no joy will remove it.
there are a few here:
believe or not,,those sounds could be dust,,bad reformat,,i prefer to wipe off drive.
also a poor defragmentstion...consider cleaning from the inside out..
Just looked and my link is back