The crackling sound of the coral reef.

https://youtu.be/eXR--I99S60

https://youtu.be/1wBYPjkGRdo

"The underwater sounds are reminiscent of static on a poorly-tuned radio, or the tantalizing hiss of eggs and bacon frying in the pan."

"The characteristic sounds come from many sources, including the rasp of urchin and starfish teeth as they graze against the hard surfaces, shrimps that stun their prey with loud bubbles produced by their pincers, and fish that pluck off bits of coral." 

https://www.earth.com/news/healthy-coral-reefs-crackle-with-the-sounds-of-busy-inhabitants/