Nature is loud right now. During the day there's a chirping and buzz-saw whine; at dusk, a grinding, droning chorus and a faint whirring sound. Marianne Atkinson, who lives in Clearfield County, Pennsylvania, says "a loud, 2 part, harsh sound, repeated quickly, sort of like saying hello" starts up at twilight near her home.
What makes these sounds?
I searched the web for an answer and found this helpful page on the Music of Nature website: the songs of 20 common insect species.
Just for fun I listened to a few of the recordings and they solved an old mystery.
Years ago, before Duquesne Light cut back the trees across the street, we heard a ticking sound at night in the summer. The bug that made that sound is pictured above, a greater angle-wing katydid. It actually made two mystery sounds: the ticking and a periodic "dzit."
When we had the greater angle-wing katydid in our neighborhood I never saw it among the leaves. If it had perched on a lawn chair, as this one did in Texas, I would certainly have noticed it!
Listen to the Songs of Insects and you might find the one that puzzles you.
(photo in the public domain from Wikimedia Commons. Click on the photo to see the original.)