Quiet fan to cool amp and preamp?

I have an Audio Research tubed preamp and solid state amp in a wall unit that is enclosed on 3 sides. Although there are no other components above or below each of them, they still heat up the cabinet quite a bit. There are about 6 inches of headroom above each component, and I can't increase it. I don't want to cut the back out either. I am looking for a relatively small and quiet fan that I can mount at the rear of the wall unit to circulate the hot air out towards the open front of the cabinet. Any suggestions? Thanks.
Radio Shack sells whisper fans for equipment. They usually come with bare leads, so you can wire them into a switched circuit or insert an in-line switch between the fan and a plug. The size and volume of air moved by the fan should be determined by your installation. Obviously, try to make sure the fan is powerful enough for your needs. If you're not going to cut a hole in the back for the fan, you will wind up recirculating warm air, so you may need a bigger fan or more than one fan. Also, the fan may generate some noise on the power circuit and in RF, so it might be desireable to plug it into an isolating power conditioner and to experiment with location to minimize RF noise. Are there any advantages to having the fan suck air in the front and exhaust it out the back? This would require cutting a hole in the back for the fan and locating the fan higher than the component versus lower than or directly behind the component if it were blowing onto the component from behind. Good luck.
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.
I had a similar problem and was running 2 radio shack fans but they were too loud. I replaced them with a component fan made by Elan. It's called the Elan Z Fan and is 17" wide and only stands about 2". It contains 2 fans and has a remote turn on and remains on for 2 minutes after the system is turned off. The fans are also heat sensitive and speed up or slow down as needed. It retails for around $250.00

I like Hermans idea!
I too looked into fans and went to Radio Shack to test drive what they had. It was a slow day and the saleperson let me test all of they had. All were too noise. I was using a friend's Rotron "Whisper" fan #027117 as my reference piece. The Rotron is pricey but it was the quietest. Specs of the Rotron are: RPM = 1600, CFM = 55, dba = 30. In my system I suspended it with fishing line from the self above. That was the quietest mod. It will also work if you rest it on a hockey puck and then place one on top. Good luck.
Thanks to all for the great suggestions. Herman's idea is the most creative of all. I will check out the fans everyone has posted.
just blow on it blow!