you could remove the harddrive cover underneath and listen for when it makes the noise. This will help to identify whether it is the hard drive or not. Hard drives have an unknown life, some can fail after a week or a month, some can last many years. It's tricky to tell. As other comments have said, the SMART utilities should say whether there is an error in the disk but may or may not. Any odd noise I hear, if I confirm it's the hard disk I backup straight away. Then at a convenient time I'd replace it to be safe. Particularly if you have data that you're worried about. Hard drives are very cheap and it's better to be safe than sorry.
If you don't store important data on it, then you can let it run on because it could continue to work fine for years, but again, hard drives are cheap