Hi fazer ,
you can reduce the speed of your fans thereby reducing the noise also
you can do this with voltage reducers , 7v or 5v you can buy them cheaply that work from a 4pin molex and plug into your fan like these,
http://www.pccasegear.com/index.php?main_page=product_info&products_id=17452&cPath=1339
or these
http://www.pccasegear.com/index.php?main_page=product_info&products_id=19592&cPath=1335
they are only examples of what you can get , you can get molex to just single or molex to more than one
If the fans are connected to your motherboard you can set fan profiles within your motherboards bios and control their speed from there
You can download a third party program like Speedfan and control the fans with the program if the fans are connected to your motherboard
you can buy a fan controller and control the fans from a panel on the front of your case