add a big fan, the bigger the more silent they are, what do you think about my fanbus suggestion? if you´re a lazy guy you can also use only one fat toggle switch to switch all fans voltages down to 7 volts ( i have a 7v/12v switch for my 8000rpm delta fan and he´s runnin almost all the time @7v)
->my 38mm delta is @7v quieter and has more power than my old ys-tech @12 volts has<- ;D