Sound in trees
I found a link with Green Tree Frog audio online. Isn't that exciting. lol It does sound a little like quacking so maybe that's the sound you are hearing Sunnysky. Hope this link works for you. Green tree frog is the first one if you scroll about halfway down. Let us know if that's it. It might be a different kind of frog or some type of cricket as Alys said or another insect. You must have a lot of them whatever it is.
Welcome to the Ozarks by the way.
Here is a link that might be useful: Frog audio