You can alway reduce the voltage going to the fans by making a fan regulator. That's what I did. I drilled some holes to accommodate three extra 12cm fans on the side of my computer panel. To my horror, after installing the three fans, I found out that my computer now makes as much noise as a vacuum cleaner if not more, so I soldered a knob and a variable resistor onto a circuit board and placed it between the power source and the fans. I made the wires long enough so I could stick the turning knob to the front of my case. Now I can rev up my fans when things get hot or quieten them down. The parts are not very expensive either. Works like a dream.
Just if you are interested, the three 12cm fans on the side of my case bought the temperature down 12 degrees idle and 6 degrees under load. Not bad for 4 hours of work!!!!
And the parts are no more than $AU20 to boot!!!