Loud Clicking noise coming out of the tank

[mike31154]

I have the same sound & I know there's no mantis in my tank because a couple of crabs are thriving. A mantis would take care of any crabs in short order. I kind of doubt mine is a pistol shrimp either, I've never been able to see it if it is. Think I may have read somewhere that even certain crabs can make this noise with their body armour.