Without a doubt, these are the quietest fans I have used to date. A standard enclosure can hold up to three 120mm fans generating 30dBA plus each. That makes for a very noisy situation. The NF-S12's in U.L.N.A. will generate around 1/5th of that. Just imagine these fans cooling a radiator in a watercooling setup; now that would be an ultra quiet PC.

http://www.virtual-hideout.net/revie...12/index.shtml

Noctua fans are popular these days, because we've got two other sites covering the same fans :

A True Review

Overclockers Club

That last review is by far the most extensive, and provides some competition as well...

I got a couple of the Noctua S12 1200 here at home, and even though they are fugly like hell, they are oh so quiet

I can only recommend those to people who wants silence.

PS: no need to use the U.L.N.A, even at 12V they can't be heard