Unusual noises from a hard drive is a good indication it's on its way out. Drives are cheap--replace it immediately. A drive can stop making the noise and continue to work for a year or more. But maybe not--it may only work for a week or maybe a day. Then, the next time you try to start your comp, it doesn't run and you've lost all your data (except for your backups, of course). With the price of drives the way they are, why risk it?