This clicking sound is annoying me

[kwirky]

About 3 times a day we hear a clicking sound coming from the tank. It's been going on for about 2 months now. I don't know if it's a mantis or not. One day my sister and I saw a snail going crazy waving it's shell side to side hitting it against the glass making the clicking noise, but I don't know if hearing it so often means the other clicks we're hearing is that same snail.

One end of the tank is a snail graveyard, too, so I'm thinking there's some sort of predator in there. About 5 dead snail shells at that one end. I put a shrimp trap there a couple days ago but still haven't caught anything.

It's getting quite frustrating. Any suggestions?