I tried to replace mine (a lot of noise and vibration) and failed miserably, the fans never turned. I ordered these from digi-key , sunon MC30101VX-E01U-A99 those are 12vd. Since standard fans have 2 wire my guess is they are not pwm capable fans, though they are driven by pwm from the board.
I wonder if its cause from unsmoothed dc from mainboard ? , or those standard fans are special?