Odd noise from an otherwise working hard drive - is it a problem?

I recently bought a new VAIO Flip 15, and have since noticed that the hard drive is very noisy. Even when nothing is being read/written, it is loud enough that I originally mistook it for the fan. I also later noticed that it sometimes makes a noise somewhere in the intersection of clicking and scratching. It definitely doesn't sound normal. The weird thing is though, it works perfectly. No problems with the laptop and a whole bunch of system diagnostics said it's fine. What do you think, does the HDD need to be replaced? It will cost next to nothing if it has to be done, but could take weeks (1 hour to change the drive, 13 days and 23 hours to get it back to me) and there are some charges if I send it in and there are no problems. Thanks!

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500GB HDD (5400RPM), Windows 8.1 (64 bit), i5-4200U, model# SVF15N190S