Quiet fan to cool amp and preamp?

I use two 4" muffin fans; one one each side of my amp drawing the heat *away* from the component. You do not want to blow the air directly onto your equipment. The above suggestion of cutting a hole in the back is a good one too. The fans that I have are high capacity 115 CFM & make a lot of noise at full speed, so I use a variac to reduce the speed to minimum required to keep things cool & they are very quiet. Right now they're running at about 90 volts. If you can tolerate very low airflow volumes then two fans could be wired in series. Or you can wire a power resistor inline to reduce voltage if you don't have a variac. Solid state motor controls are electrically quite noisy so that approach is not advised.

There's a fan in my integrated amp that is VERY quiet... I have to put my ear 3" away from it to hear it running. The fan itself is an "NMB" model # 4715MS-RT-B10.

directron.com sells pabst fans. they are only 12db.

I have my wife use a folding paper fan and wave it over my amps during listening sessions. Very quiet and inexpensive. As an added bonus, I can send her to fetch a beverage when needed. Of course, if she ever logs on to this site, I will be listening to the sounds of silence while I sleep in the garage.

I have seen some good looking and quiet 19' rackmount fans for computer servers or studio equipement. the nice thing is they have a power switch and come in 1U and up the nice thing is they usually multiple small fans so you can run them at low speed to get the noise down and still get good CFM. I see them on Ebay frequently.