I can't say this from personal experience with the GF4, but the 8500 is very quiet, and the GF3 wasn't quite as quiet (to my knowledge, posibly not noticably). The GF4 fans have been described as moderately noisy to "Like a mini-blowdryer".
Now, I have not heard any official numbers on any of this, but I do know that with every other fan quiet in my CPU, my HD makes more noise than my 8500 fan. That's pretty quiet.
I do not like it Tom you see,
I do not like green PCB.