I had 3x S3 running under my desk in my room and coild happily sleep with then running. I boight an S4 with the intention of incresing my hashing power but it was like a jet engine. Had to keep it in the adjacent room and it was still louder than the S3's
Try and go for S7LN models or underclocked S7's and change the fan speed to balance noise and cooling. Thats the step i took and worked great.
that's what i was worrying about. :/ Maybe a fan replacement? Or would they overheat.. I was considering pulling them out of their enclosures and putting a custom fan thing.