that does not sound like a hard drive to me, it is much more probable that it is either the fan, or the cd/dvd drive. my money is on the fan. this is something you want to get fixes asap, i would advise that you dont use the computer for extended periods of time until you replace it, as a hot cpu wont give you many second chances. if its the fan you can fix it for a few loose coins.
if it does turn out to be the hard drive (they normally make a tap tap tap or motor sound) then its a sign that it will die soon, how soon i cant say, i have had hard drives make funny sounds at me in the past and then be broken within the hour, and i still have an external one that sounds like a lawn mower, that started making funny noises about a year ago and stil works.