Leonidas --
The other user's advice was correct: hard disk OR fan. The former spins really fast, so noise is likely to be high frequency. The fan much slower, so lower frequency noise.
My old dv6000t laptop had fan noise. The adhesive on the part number label came loose, and the label was flapping around in the fan blades (like when kids rig their bike with a playing card so it flaps against the spokes).
Unfortunately, to get to the fan on this model, I had to remove just about everything. I used to be a tech, so I have an anti-static mat, and much experience with very small parts and small connectors. Unless you are similarly capable, it's best that you sent it out.
Good luck,
John Kwasnik