Manure sound (flies) and gnat sound persist after manure/gnats are gone

Frequently, picking up manure does not stop the sound of the flies, and the sound persists even though no manure is on the ground anywhere around. Same for guano. And also I discovered that killing gnats does not always stop the sound they make. I can tell that the sound is tied to the empty spot where the gnats/poop used to be because as I move around it,it gets louder and goes from side to side accordingly. The sound is definitely assigned to the space where the noise-making thing used to be, but no longer is.