pics!
Discussion
Nothing fancy! You can see the fan is just barely larger than the opening, but that doesn’t seem to matter. I think keeping the airflow less restricted might be part of what helps the noise. Also possible the adapters cause more vibration if the airflow of the two fans are at all out of sync but they are both being forced through the same opening. Am still a bit shocked at the comparisons 
Also, it doesn’t seem like a huge difference, but here is the Braiins dashboard for the bungee vs the 3D printed adapter. It’s only a 200-300 rpm difference, but any increase over 1200 becomes VERY noticeable in a bedroom. The sound profile also seemed a bit harsher with the adapters - not sure what caused this. 
wow, I run my s9s at 700 too - had to double take this because it looked like mine. I run stock fans, will compare tomorrow
I did also replace the psu fan with a noctua. Doesn’t impact this discussion but makes a big difference in sound. Right now I’m about 6 ft from it running at 700 and my iPhone is reading at around 37 db. I don’t know how accurate these apps are, but it is quiet enough that my wife is able to sleep which is all that matters.
looks like those fans do make a difference. this one runs in a room void of rugs, sitting on hardwood. 
You could try upping the target temp (mine is at 94 C) to see if the fans have to work less, but I bet this is primarily a difference in fan size 140 vs 120 and noctua vs stock for the db level.
I probably should keep it off the carpet honestly, but I have found if you stack the miner with the PSU on the bottom and add some rubber padding the ground will barely get warm from contact during normal operation. 
I have the miner rotated 90 degrees from how I normally run it above. Hopefully I’m not doing something incredibly dumb here
I am super excited to see what you get with stock! I am using the NIOSH app for sound measurement though I’m sure our comparisons won’t be exact since the mics aren’t calibrated.