Ahah! D'oh. Well... hmm.
Alright - Main-> Driver Settings -> System Settings -> Fan, direct control I have three sliders, 'standard 2d, lower power 3d, performance 3d. The only slider I can move is 'performance 3d', and setting it to 75%, well...
Fan RPM is 4856RPM. And still loud - the RPM does fluxuate by about 100RPM at (what I think is) random, regardless of what I force those fan settings too, though always above 4000RPM, and always /really loud/.
I hope I'm getting close to a solution!