That's the sound of thousands of snapping or pistol shrimps snapping their claw. The noise isn't caused by the claw itself, but by a bubble formed when a tiny jet of water gets expelled from the claw at 100km/hr! The speed and low pressure turns the water into super hot  steam (4000C!), and when the bubble bursts it makes that clicking noise. At 250dB it's louder than a jet fighter! Sound courtesy of Detlef Lohse, full story here: https://www.youtube.com/watch?v=ONQlTMUYCW4 

Sounds of science: Snapping Shrimp

ABC Science