One great brand for fans is cougar. I use their fans in my case for the front intake and the exhaust as they have the highest RPM and move the most air while having the quietest level of sound. They are still audible, but what I found is that if you combine them with a fan controller and you limit them to a bit before max speed, they really quiet up. Take a look at their fans, I am using one of their Vortex series, but they have other fans as well. They make them in 120 and 140mm.