No such animal as the internal heatsink layout of them prohibits it. They require not only high CFM but also have that flow delivered at high pressure to overcome the internal resistance and that = LOUD. Search the s7 and s9 threads, this has been discussed to death in them.
However, that said: At least the s7's can be under volted/under clocked and that in turn leads to fairly quiet operation. Search for Sidehack's thread un undervolting the s7.
Thanks for the info! I guess this puts my quest for the perfectly silent miner to bed.