clicking sound in tank

[GMGQ]

Y'know, I've had clicks in my tank before I even got my pistol shrimp & striped goby.

For the longest time, I thought it was a crack under my tank, and droplets of water were falling onto the foam under the tank. But then again, there's only about 1" of space under the tank and around the plastic frame, so a droplet of water shouldnt have enough distance to make that noise.

Of course now that I have the pistol shrimp, I just tell myself he's the culprit. What sucks is that the pair are under this LR that's behind another piece. So I can only see them occasionally when I peak behind the LR in front from the side of the tank :S