If i was lucky enough to have that mining rig, make about 600.00USD a day, my problem would be a persistent shit eating grin and a constant hardon, noise would not be a big issue.
End of off topic comment:
That being said, have a look at Coolink fans. I have a Norco SS 500 5 in 3 HD hot swap bay, that came with a really noisy 80mm. Swapped itout for a Coolink and its whisper quiet now.
http://www.amazon.com/Coolink-120mm-800RPM-8-5dba-SWiF2-1200/dp/B002IG5HFW/ref=sr_1_12?ie=UTF8&qid=1374626248&sr=8-12&keywords=coolink+fan
Not sure what rig you are referring to. Bfl Single 60Gh pull about $90 a day before electricity cost at current difficulty.
I meant to say 600 a week.