Quiet fan for rack cooling installation?

Try a small muffin fan from radio shack or some electronics supply house. They are pretty quiet, and made for cooling electronic equipment. They come is a variety of sizes, probably a 4" would be good for your application. You may have to run it off a wall-wart supply.

Try www.pcpowerandcooling.com that make some small fans that are about 20db and cost about 8 dollars each with free shipping. You will have to go to radioshack and buy an AC/DC convertor for about 29.00. The fan has a red wire and a black wire. The converter has matching connections. Run wire from the fan to the converter. If you need to cool other equipment, buy more fans as they only draw a little amount of current. I have 4 fans running off my convertor.

Not sure if it would work but www.quietpc.com has some computer fans that are supposed to be quiet.