happy reefer, its difficult to speculate what causes the tick tick sound unless you have seen the mantis shrimp. It is high chance that there is one of them in the rocks but unless you see it we cannot be sure. Piston shrimps also makes the sound, turbo snails also makes the sound etc.
But yes, if you really do see one of the mantis, then take out the rock and leave it dry for awhile, that fellow will crawl out instantly because it needs water. No need to dip it in fresh water (At least that's how I caught mine).
They take out the small fishes when they grow big.
Lester, I will upload a picture of my trap pest box this evening probably.