On the recording, you’ll hear some birds, some individual cicadas and then the entire background susurrus is the Brood X horde singing.
They started emerging over the last couple weeks but this weekend they really started swarming. There’s entire tree trunks in my neighborhood coated in them.
I live in an area that hasn’t been touched in decades, lots of old houses with established landscaping. So they’ve just been chilling underground for the last 17 years and at least a few generations have been able to do the same.