Originally Posted by Chargeit
I'd avoid filling up every fan spot and instead try to keep an airflow path (try to avoid having fans fight each other). I'd look into hooking the fans up to a controller or your mobo. I run my case fans off my mobo and usually have a fairly conservative curve set. A well set curve can go a long way to keeping your fan noise under check. I normally set a max fan speed of 80% on my case fans and even lower on my cpu fans.
Worth mentioning pretty much all fans will get annoying if you allow them to hit their max. I don't see a reason to go for silent/low rpm fans when you can get good higher rpm pwm fans and limit the max fan speed. Those Noctua's are really good fans but make sure to limit them to 70 - 80% otherwise they'll sound like jet engines.
I nearly went and bought $ sound dampening material, when i found it was possible to tweak the fan speed in the bios a few weeks back. No need to hit 100% fan speed when not necessary. Great advice.