I can imagine your house chirping and tweeting about, when suddenly you wake from a deep sleep saying "what was that!" when some unusual pattern of sound happens.
The pattern matching and decoding portions of our brain never, ever, stop their efforts and are wired deeply in to the survival mechanisms we have.
Intriguingly, on a single night I experienced some sort of hypnogogic auditory hallucination that caused the sound to lose all familiarity. Instead, I perceived the sound of a male singer arpeggiating rapidly. I found it highly disturbing.
fwiw, the only thing that works well for me is masking any other sounds with a mix of grey and brown noise on top. i use 'white noise app' to achieve this, and it helps me get to sleep, masking out many other ambient disturbances (road/car noises, mostly).
Smoothly running stream? Everything is green. Rapids? Yellow-status; something needs looking into. Waterfall? Something's gone terribly awry.
Happily chirping birds? Successful health checkins. Monkeys screeching? Unhealthy result. Jaguar growl? Datacenter is on fire.