That is the sound pecans make when falling onto our roof and hitting the ground outside here in Hyde Park. It happens all day and all night long - but not in any mind rattling way. It is a very pleasant sound, in fact.
It is the sound of Autumn in Austin.
You can pick these nuts off of the earth in abundance around these parts and eat them right from the shell. There is never a shortage of Pecan Pies in town.
Should we ever find ourselves in a far away new city in the future I predict this will be a sound I will miss.