Seriously though, I have a Thermalright X-Silent 120 in my ATCS 840 and it's a superb fan. It doesn't seem to move as much air as my Gentle Typhoon AP-14 but it moves a decent amount of air and is dead silent.
I've heard from several people that it can have ticking/vibration problems if it's mounted horizontally. I have mine mounted as a bottom intake and I haven't experienced any issues (The rubber mounts might help) but it's something to keep in mind.
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