What animal makes this sound?

Factual Questions
1

I was noticing tonight how the local somethings in trees were really numerous and active, (after torrential rains a couple of days back–they are always very active after rain in warm weather) overwhelming the local fireworks. I had always assumed that they were tree frogs, but decided to look up which. I found that the calls don’t match either of the two tree frog species that I’ve actually seen here (the Gray tree frog Hyla versicolor and the Green tree frog Dryophytes cinereus) so now I don’t know what they are. Some different type of tree frog I have somehow never seen? Some type of cricket or katydid?

(Upstate South Carolina.)

2

Aren’t they just cicadas? The exact sound varies among species, there are a variety of them in the youtube video halfway down this page, jump through it to hear different sounds:

3

I don’t know–it is nothing that I’ve ever thought of as a cicada sound.

4

not surprisingly, there is a website to check out and identify cicadas by their sound

5

Sounds like a Slinky to me. Is there a large staircase anywhere nearby?