Good concept, but plot weakness

Rating: 4/10 (6 July 2018)

This film starts off well, setting up a world where vicious aliens that hunt via sound now roam the earth. They seem to be amphibious, so there's no safe places. The secret to survival is to stay quiet--but it's okay to make noise near noisy things, like a waterfall, which will drown out smaller noises. So far, so good. This could have been good.
But it's day 473, so a year and a half in. The family we follow has adapted. They have a bunker in the basement filled with TVs monitoring for creatures approaching. They have light strings hanging over their farm's paths so they can see at night. Where's the power come from in this apocalyptic world? Perhaps they have solar panels we didn't see.
On the stairwell into this basement, there's a nail sticking up through the stair tread. Why is there a nail there in the first place? What was nailed down in the middle of the stair? It doesn't make sense. And why, in a year and a half, didn't someone take this hazard out? Why didn't mother stop to see what her clothing sack was caught on? And how convenient to the plot that the nail was bent straight up by this! I ask: couldn't somebody contrive a better plot point?
And if this is a year in, how is the corn planted in rows? Is this farm a test bed for perennial corn? Because corn's an annual, so it looks like this little, survival-mode family planted acres of corn for themselves, all in neat rows. (The tractor is off limits because it'll bring the invaders.)
Additionally, miles of sand paths have been laid down on railways and roadways. It's quieter than gravel, and easier on bare feet (which are quieter than shoes). Where'd the sand come, how was it dig so quietly, and who had the time? Dad must be incredibly industrious, all while being super quiet.
And beware the corn, because when it's in silos and the kids fall into it, it might be quickcorn--it's like quicksand that sucks you down, only made of corn. Until the monster falls in; that property then shuts off and it's a normal vat of corn.
It eventually unfolds the creatures use ultrasound to "view" their surroundings, and it's an exploitable weakness. Finally, our heroes might have the upper hand now--because though humanity knew early on that the aliens hunt via sound, none of the billions of people across our planet thought to use noise as a weapon. Thank god serendipity hands us answers, because we couldn't have figured that out on our own.
The production values were good, and the movie did carry a spooky feel, but the plot had too many blatant holes to be believable.