Im running 5 of them in my case, 4 via a PWM splitter cable, two as cpu cooler fans and 2 as top exhausts. The other is a bottom intake. At full speed they are quite audible, but thats only in high stress testing. In normal use they ramp down to 800 rpm ono where theyre inaudible. The PWM function speeds up/down the fans according to load. Ive read good reports on the gt's, actually had a few a while back but never used them as i didnt like the colour scheme, besides due to their corner design they wont fit on my k2 cooler clips.