Quiet 40x40x20mm fans needed

Evening all,

I've got a switch which is fairly noisy - its well spec'd but makes too much noise. Would be fine if it was in the loft/garage/datacentre, but it isn't. Looking around at alternatives they are all a lot more than I paid for this one, so I'd rather see if I can make it quieter.

If I were to replace the four 40mm fans in it with some quieter ones, it would be perfect. I have tried some of these: http://www.scan.co.uk/products/40mm-...inc-fan-screws which are quiet enough, but only just about push enough air through the switch. They are only 10mm thick though. I'm guessing by moving to 20mm thick fans they are likely to push more air for the same number of RPM.

I don't want cheap fans I have to replace every five minutes, but by the same token I don't want to spend a fortune on them either! So, what would would you knowledgeable HEXUS folk suggest?

I cool a Juniper SSG5 and 24port fanless 1810-24G switch with one slow-running 120mm fan, positioned on top of each other with a gap so that the central no-airflow spinny bit of the fan is avoided. They only need very slight airflow to run cool.

Also, as a PSA while I'm on the subject of DIY cooling: the grid of vent holes on the sides of a Smart-UPS 750 are arranged in such a manner to allow a 92mm fan to snugly latch on to, with two slightly protruding bolts on the top two holes.

These ones are pretty good http://www.scan.co.uk/products/40mm-...set-cooler-fan and do move more air than the 10mm thick akasa version and are low noise, not sure how they compare to the fractal design one as I've not tried it.
You could always add a resistor link to it to slow it down a bit if you think it's too noisy http://www.scan.co.uk/products/shark...m-and-noise%29 (I'd go with that over the zalman one as it drops the voltage down to 5v which I think would drop the rpm too low and reduce the air flow too much.)