Not to get into it too deep, but the whole thing about noise is both quantitative and qualitative. Some kinds of noise are more objectionable and noticeable than others at the same or even lower levels... the higher the pitch, and the narrower the band, the more generally objectionable it is, provided it's within the normal hearing range... if you've got to have some noise, and you do, then broad spectrum midrange white noise is easily the least objectionable, particularly in urban environments where there's a lot of it in the background, anyway...
And, yeh, the zalmans are excellent coolers, and very quiet, if you're willing to spend the money for that extra little bit... I've heard and read good things about the arctic cooling products, too, although I have no experience with them...