Hi,
I just installed 2 of these fans on a NZXT Kraken x52 in an NZXT H200 housing.
I start hearing the fans from about 50-60% power. The fans get really audible from 70% upwards. Remember, I have two of them, and these are on a radiator, so under pressure.
I'm sorry I can't give you the RPM, the fans are connected to the pump, which doesn't give me e ability to see it.

Difficult to answer because it is dependent on many factors, Get in touch with me, asidscript@gmail.com (also for skype) as well as daniel kritikos. https://www.facebook.com/asidscript, https://www.youtube.com/user.... I maintain datacenters by day and build gaming rigs by night. Lets talk about this fan situation, I can help. Regards
Dan