[obso1337]

I had this problem too but instead of using a 40mm fan i use a fat 120mm and stand it upright at the bottom of the case, so that it blows cool air right over the north bridge. I also connected a zalman fan controller to it reduce the speed. This makes it really quiet and you don't need it to run too fast to keep the chipset cool. Using 120mm fans are normally much quieter than 40mm ones anyway.