You might have to turn the volume up on your computer to get a sense of just how loud these things can be in real life.
This is cicadas with a bit of spider monkey in the background:
This time with howler monkeys:
And with a local guide:
I always thought they made the noise by rubbing their wings together, but according to Wikipedia, they have a stiff membrane in the abdomen which clicks when pulled out of shape by the cicada’s muscles, and again when allowed to return to the original shape. The sound is then amplified by a partially hollow body.