It's been refreshing to have the windows open at night but then there is often some external noise that wakes me up.
One night I heard something of the wild animal variety walking around in the creek. Tromp stomp clomp, nuffle rustle scuffle shuffle. It scared the birds roosting in the trees and they started to squawk. They are some kind of egret, but I call them pooping cranes because they leave such a mess on the ground. I think they literally had the sh!t scared out of them that night.
Another night it was a broken sprinkler. I got up and went outside at 3 a.m. to make sure it wasn't in our yard. We've had all the sprinklers in the back yard turned off at the valves for over a year, but you never know if a pipe has burst. Luckily, it wasn't us, it was from the apartment buildings behind us, those water wasters.
After that, I decided to close the windows.
Of course the cats are active, so I can't eliminate the noises inside the house.