Well I know theres the option to have it on at all times but you really dont need it on all the time. And I never hear my 7800GTX over my case fan so I figured the 6600's couldnt be too loud buy maybe they are.
Actually I dont even hear my 7800 when I open the case and put my head up to it, but thats probably cuz my rear case fan is kinda loud, need to get a quieter one.