if its anything like the typical pc installation the fans will be temperature sensitive and spin faster when its hot and go slower (and quieter) when its not hot.   since its likely that most people will want it to overclock to the max, and run very hot i think its safe to assume the fans are going to be spinning pretty fast all of the time.  but if the noise is really a problem you can always under clock it and have a quieter but less profitable system.  (no one's going to seriously do that are they?)

the only reason you can run your bitfury's without a fan is because they're not running that fast, or your ambient air is very cool.

you could always switch out the fans they give you with quieter ones, but they probably won't perform as well so you'd almost certainly be crippling the performance if you do that.  you make a choice, fastest possible, whatever the noise... or, low noise and lower performance.

im not expecting either hashfast nor cointerra systems to be as quiet as knc systems.. simply because the amount of watts of heat that needs to be dissipated is a lot more... that said, i suspect they're still quieter than avalons.

in noise per gigahash i am expecting both the hashfast and cointerra systems to be very efficient (considering their performance).  but in absolute terms, they probably won't be silent!   cointerra's has a larger radiator (almost the full size of the rear) so that may give them an edge in not needing as fast a fan speed, but until we see both systems running... and hear them... we won't know.

and anyway, both these systems deserve to be run in a data center!