I am absolutely thrilled, I've had it with PWM control and under Windows it is not audible! My claim was to achieve a silent operation level with good cooling. And this ingenious Noctua A15 stem exactly where many others tried cooler fail. I'd this fan subjectively quieter than the "Be quiet Shadow Wings 2 140mm assess with max 1000rpm! The Noctua produces a pleasant flow of air with no distractions like Klacker etc. The package is very generous and convinced processing. BUY recommendation, worth every euro!
Update 08.2015 I'm still very pleased with this class fans. Really great the thing;)