Here is a link to a very good web site with a lot of information about silent pc's. They've got a list of recommended fans:http://www.silentpcreview.com/article63-page2.html
Unfortunately they do not have 140mm fans on their list. Generally speaking the 140mm fans run a little bit slower than 120mm fans but still push the same amount of air. The end result is lower noise. My Dragon Lord case came with three 140mm fans. Those fans are much quieter than the fans on my cpu heatsink and video card.