Are you sure the sound is coming from the hard drive and not one of the fans? Just to be on the safe side I would make sure all of your most important data is backed up.
Another thing you can try is go to the website of your hard disk manufacturer and download one of their diagnostic tools. Most of them have diagnostic software for their specific drives.
If it's clicking it's bad. You should run Samsung drive testing software, but really not necessary replace it. BTW there is nothing wrong with Samsung hard drives either and replaced with a Maxtor, will fail much quicker.
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