Fan Speed of a 2-wire fan

I recently bought a 25x25x10mm fan (Sunon KDE0502PFB1-8 from Cooler Guys) for use in an external hard drive enclosure.

Upon installing the fan, I found that it is pretty loud. Is there a way I could install some kind of controller that would control the speed (i.e. lower the voltage of power supplied to the fan?), thus controlling the volume?

That way, I can turn the fan down and still have it in use, and turn it up when I'm doing something that requires heavy usage on the drive or if I feel it getting too hot.

I don't mind drilling into the case of the drive or anything - but any control needs to be about the same as the fan (preferably smaller).

buy a fan speed controller. you can find them relatively cheep ($10-20)