Unfortunately if you add a lot (or any in my experience) of tower cooling it starts to get really noisy (100+ case fans - wtf???).
Any fans tend make the white noise really loud - especially case fans when the ingress/egress is generally just a set of holes drilled into the case you can get some really nasty frequencies of noise produced.
Perhaps a good way to accomplish this would be to cut out a circular 70mm hole in the rear of the case, allowing the fan to move the air with less turbulence.
Personally, I'd experiment a bit before hacking my case apart though.
