I posted this earlier in the thread, but I think it got lost in the excitement of new S9s. With the original S1s, there was a mod that worked quite nicely.  You could take them apart and put a 200mm fan on each blade to cool them effectively but silently:

https://imgur.com/a/RUAX5

I did this with my old S1, and it worked amazingly. The miner ran at full speed, with a better temp than the factory fans, and it was totally silent unless you were standing right next to the fans. I'm going to wait another month or so until my warranty expires, then I'm going to try the same thing with my S9. Particularly with the thermal throttling built into the S9s that protects them from overheating, I'm confident this will make for a better mining experience. My only concern is finding another "base" for the third module in the S9s.