I just installed an optional 120mm fan on my cooler master evo. For some reason its idles at 1800rpm. At that speed the fan is really loud. I've checked my asus maximus hero bios and there is no option to lower the optional fan speed. I'm able to adjust the primary cpu fan with ease.
http://i.imgur.com/pEXRG4b.jpg
http://i.imgur.com/4Hci9XD.jpg
http://i.imgur.com/ZGOejOF.jpg
http://i.imgur.com/pEXRG4b.jpg
http://i.imgur.com/4Hci9XD.jpg
http://i.imgur.com/ZGOejOF.jpg