Sounds definitely more like a fan to me. Also, as was already mentioned, even a wire that slips a bit and now sits up against a fan will make that type of noise.
Open up the case and you should be able to find it right away.
Or if the hard drive is in a removable tray with a fan, those are notorious for noisy fans, I have to oil mine at least once a year with graphite and oil.
You can do the same with case fans and even cpu fans. You can get graphite in a small tube, kinda like a syringe, and just about any oil, actually you can get oil in the same syringe-like tube.
Peel back the label on the fan and put the graphite in first and then the oil, just a bit of each, then start the computer and give it about 30 seconds to work in and all will be well.
Dont put a lot on and be careful of graphite, it stains badly, worse than oil.
Also, if its the fan for a cpu, best bet is to oil it and then go looking for a replacement asap. For the others, just graphite and oil and thats it.
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