Snapping noise - driving me nuts!!!!!

[i have crabs]

usually i would guess pistol shrimp unless other signs like dead crabs and snails,
i once bought a pistol shrimp that was so loud i couldnt sleep and i had to catch him and take him back after a couple weeks.
so far all the snails and crabs seem to be alive but i did have 2 pepperment shrimp dissapear but after checking out the tank non stop and not finding anything i gave up and if i didnt see the mantis with my own eyes i wouldnt believe it.
sofar the trap only catches mystery wrasses.