At full speed they are loud but move lots of air.
I use PWM control for my case fans too but my mobo only has 1 PWM socket.. the CPU fan socket so I use a PWM splitter with molex power like the splitter Thermalright supplies with SA SB-E Extreme. I assume you are using it on your cooler fans.
My fans run 660-800rpm most of the time with temps in below 30c... 1050rpm at full load when rendering and below 50c on my 980. I'm setting up another system with my 920 under SA SB-E Extreme and plan to overclock it as much as possible. Hope to get 4.2-4.5GHz