Calm down. Tons of thing can cause clicking noise. Lights going off, stealth heaters, Snails on glass next to powerheads, even clown fish. I doubt that it is a mantis if it is on after lights out though. Most mantises are diurnal. Day animals. I don't know about pistols though. Until you see some evidence (snails or hermit shells with holes in them, the animal itself, shells piling up in one place etc.) it is premature to think that it is a mantis. Especially with no mortalities.
I'm still pretty sure that it doesn't exist, but if you decide to use the bottle trap don't use soda bottles because they leach chemicals into your tank and may kill the mantis. Use a water bottle. Also many people on the mantis forum would want this mantis that I don't belive in if you catch.