Upon world generation, random blocks in the ocean will break, playing the stone breaking sound, and showing blue water breaking particles. There is no player interaction, and the presence of kelp does not cause the bug.

Attached are screenshots of the breaking particles and with their visible locations. I was not able to record game sounds with my setup, but you can clearly hear stone breaking sounds all around the spawn island.

This was not reproducible in prior snapshots (18w46a,b,c), leading me to believe it is a new bug.