My first thought was........
he ain't right.
Blow your horn.
Piss poor planning to try something that monumental, delicate, and dangerous and not have some kind of noise abatement plan for the town like round up every swinging richard in town and keep em together so you can make sure no noise was made. Then I remembered this was actually supposed to be a dry run. Seems the writers thought of everything.
Then on the other hand, why didn't sasha et al lay down on their horn, start shooting, whatever to compete with the distant car horn? Also they had these suckers in a pit that apparently they could not negotiate except that one narrow exit. They have heavy machinery. Why not excavate, dig, block, put boulders in the way, whatever, to keep the things in a very convenient, trap/holding pen.