yeah an s9 doing 1 board can be very quiet.
does 3-4 th pulls 300-350 watts
I have a thread on how to build
and someone riffed on my idea and has a thread on a better design
I also did some testing with a m10 and 2 boards.
set to low.
lastly there is a guy here selling a 2 board s15 which may be exactly what you want but you will need to supply 220 volt not 120 volt.
https://bitcointalk.org/index.php?topic=5232832.0if you have 220 volt power his 2 board s15 set to low may be quiet enough for you