I understand the hear you (pun intended...
).
I would think that I would prefer to get a new S9 and run it at full capacity, therefore, i believe the approx db level unabated is around 80db.
So hopefully the effort/costs involved in building an enclosure to reduce the noise would be minimal in order to utilize the S9 at its' full +/- 14Th/s rating, even though I just plan on being a small home miner.
Right now, I believe this is the only major hurdle I need to overcome before I decide to do this.... hopefully no other significant issues pop up in my planning/implementation.
I have 100% solar at my home, so my current elec bills are just the taxes/fees and total home surge protection charge totaling about $20/month. I know I will be using more than I currently generate, but I do not see my electric costs rising too much based on the S9s consumption.