Snapping sounds in my tank

[Canadian]

There are a number of things it could be. Mantis and pistol shrimps get blamed most of the time. But I've heard similar noises from clown fish that will making a snapping sound with their jaws from time to time. Additionally, I discovered earlier this year that blue leg hermit crabs can make similar sounds as they attempt to violate each other for their shells. I was sitting by my tank and heard that dreaded clicking sound and jumped up to see what it was. I discovered it was a hermit crab violently tugging on another crab trying to evict it from its home and hitting the shell on the glass of my bare bottom tank.