I am using the same fans as you (minus the LEDs) in my main system and up to about 500rpm they are basically inaudible, at least to my 43 year old hearing. Even at 1000rpm their sound is very benign, ...

NMB Minebea has developed a range of low noise fans. In almost all new developments for Home and Office applications the noise of the fan is a great deal of annoyance. High packing density and high ...