Hmmm, the only real issue I had was the electricity, but i just figured they had a
Zacharias thing going on and had built some kind of generator at the falls. The father's situation room was a significant power drain, but who knows what kind of off grid solar, wind, hydro, etc setup they have.
It looked to me like they tried extensively to lessen noise (sand in the house and on pathways, rolling dice on blankets, creating a sound canceling baby chamber, sound canceling basement, etc). It seamed like the house itself is a sound dampener, which can explain away why a certain scene in the house doesn't attract the monsters.
Wasn't the nail initially bent over and then when she did the laundry it snagged on some clothes and pulled the nail point up? They can't exactly wrench it out.
I personally felt the sound design was great and increased the immersion of the world being created. I also like movies that don't completely wrap themselves up at the end. In terms of doing things that create sound, I thought that was a main plot point of the movie. They are trying to fight back at the world they've been dealt by living as close to normal as possible. They still play games and go on outings, but they've adapted them. There's a certain scene with an old man that I think they're fighting against his psyche.
Maybe I'm just a light weight when it comes to cinema and story telling, or rational thinking, but I loved it.