Not even quieter than others.

I have now tried some fans:
Be Quiet! BL030 Silent Wings 2 PWM
PH-F120S Phanteks
Scythe - 120mm - PWM (low budget about 9)
From storage ago the fans are all great. All have a very smooth running.
The noise is generated only by the airflow.
And with every fan. at one maybe a little more than than the other.
But they will be heard for me all from about 700 U / min.
And clearly audible from about 1000 U / min.

My tip therefore: Who would not necessarily need masses of fresh air in Gehäse and want a quiet computer, which should be already set a fan with a good camp. Speed ​​should be as low as possible - up to 1400 rev / min.
Then you should have a Board that a PWM fan controller has.
Then you can adjust everything according to his preferences.

Another variant would be:
no PWM fan, and for every fan knobs (there especially for computers in every online commerce and are also easy to install) or buy a kompltte fan control.
And then one realizes that the hard disks do anyway most of the noise;)
But for there are solutions (are best for the homemade).
Had I previously - is also very good.