SilverStone Ultra-Quiet 140mm and 120mm PWM Fans @ PureOverclock
 

“The quest for silence is an ultimate goal among the elite of computer enthusiasts. Some people take this quest to the extreme in having fanless computers, but even the slightest airflow can be inaudible while making a huge difference in temperatures. That’s exactly where SilverStone comes into the picture with their new series of Ultra-Quiet PWM fans. Rather than trying to break airflow records, these tools are designed to operate at a such a low level that you won’t be able to tell if they’re spinning unless you look at them.”

http://www.pureoverclock.com/Review-...m-fans-review/