I've got an 18db Silenx Ixtrema Pro IXP-76-18 120/38mm fan right next to me and can "confirm" that the noise is way more than 18db.
Also I've got the feeling that it is not as powerful as I expected. From the sucking side I feel also air getting pushed away...
So, I think this fan is not worth the ~20 Euros I paid for it.
I'll probabaly try the Noctua NF-P12, because I need them for my radiator.