clicking sound in tank

[christyf5]

Hmm, no trochus snails, sandbed or sand/rocks getting sucked into powerheads. I've noticed it every morning this week when I come down to the computer and the lights are still out. At first I figured maybe it was my PVC nori feeder clanking in the current but it wasn't in the tank, I've searched a few times but to no avail. All my fish are accounted for but I have had someone munching on various zoo rocks over the past few months. I thought it was el monstro crab I got out of there awhile ago but the zoo munching has persisted. Guess I'll just keep looking. Hopefully its a pistol shrimp of the harmless variety. Either that or my wrasse finds him soon