tick tick tick

[amazingbobby]

The tick tick tick sounds I hear from time to time broadcasting from my reef aquarium.....pistol shrimp? Mantis shrimp? I have read many other posts but am unsure in my case. I hear this sound mostly in the evening, but have in the early morning.

Have not seen anything unusual, and no dead livestock with the exception of an Ocellaris that died of unknown causes a few weeks back.

What evidence can I look for, CSIs, to determine what is making the sound?