system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The sensation of "too quiet"
gpt
Just spitballing, but human brains filter a huge amount of information all the time, to include ambient noise. We usually don't think about it because it isn't relevant to any of the decisions our brains think we're going to need to make soon. The sudden absence of noise, however, is unusual. It breaks the pattern, and our brains tend to notice that. They also tend to jump to conclusions about what the pattern break means.

Specifically in the case of silence, your brain is probably reverting to a fight or flight response. Sudden silence might mean that there is imminent danger in the form of a predator that everything around you has noticed (and is hiding from). Your brain assumes the worst, so it starts raising your hackles. It makes you hyper alert so that you can run like hell if need be.