I would ditch the "box" altogether if I were you, the noise that you hear a few buildings away is the effect of the high rpm, it comes from the fans, not the miner itself, and then you get that whistling sound which is the result high-speed air passing through the heatsinks, the fans need to spin at a higher RPM because they need to main a certain CFM with those small blades, so the best solution would be to get a fan with bigger blades which could move the same quantity of air at a much lower RPM.
Now that larger fan will still make some noise which is nowhere comparable to the stock fans, but you could still reduce that sound even further by installing a duct, however, since more duct = more resistance and heat trapped, you will need a larger fan.
Here is a video you should watch https://www.youtube.com/watch?v=8JJHSj-F0yI