Arboric Ducts

Why is it you can be in the middle of the woods, miles away from even the nearest 2-lane highway, and still hear cars? They can sound like they're just out of eyesight. Knowing they're miles away, some freakish phenomenon makes it still sound and feel like they'll come barrelling through the trees any second.

You'd think the trees would be a good enough buffer. The distance, plus the obstacles, seems like it would act as a decent muffler. Somehow, no, it's not.

Not every vehicle sounds loud enough to break through. It's like some sort of arboric ducting. A random vehicle can hit just right to travel through miles of trees and brush to hit just right on the eardrum.