To reduce the speed of the HDD (to reduce noise)?

If there is something worth contacting tech support. Neoficialni utilities risky to use.
IMHO more reasonable to deal with noise isolation at the enclosure level.

There is such a thing — AAM, Google this term and find a utility which can change the level of noise, but I warn you once — to the detriment of performance. And look does the noise, which you want to get rid of (since the normal hard work is rarely heard by themselves) as a result of vibration, then you will help an insulating gasket between it and the housing.

Programs of type MHDD and Victoria allow you to control AAM, though not all drives support it.

Once upon a time interested in this question. On the old Sigaty could set utilico (even Dozovuju) change the performance/noise, but then her site was removed and a new series of hardy it no longer worked. As it turned out, the patent for Acoustic Management was IBM, now accordingly, Hitachi. I assume that the firmware of hard drives still somewhere remained able to tweak, but in the formality and accordingly the correctness of the method guarantees no one will not give.
\r
PS: In the faq on the website of Sygate to the question "is it possible to reduce noise at the expense of performance?" was given a terrific response — "we produce only high-performance hard!"

From hdparm -h:
-M Get/set acoustic management (0-254, 128: quiet, 254: fast)
It?

Then you need to decide that going to reduce the revs or the noise? After all, the concept is not quite identical ;)
Acoustic management reduces turnover, and the algorithm fidgeting heads, which screw is quieter or louder in the operations of VV/vyv. ;)

IMHO if you want to reduce the noise, then there is no solution better than silicone washers. Cheap and cheerful.
There are plenty of 5" rekov, reducing noise — but in fact it is the same.
\r
If the requirement is hard, you should think about how to buy a low-noise disk.
It can be either any modern slow-speed disk — or just a successful model for 7200.
Seagate Barracuda ES.2 is a perfectly respectable option.
If money is a wagon, and a lot of places do not, then you can even buy a SSD.