3 Clicks and a shuffle

[Rev_Svejk]

I've got a 60litre (15 gal) cube just up and going 4 weeks now. It's got a couple cleaner shrimp, a diamond watchman goby, and a small black ocellaris (yeah I know I probably stocked too fast). I started with about 6lbs of base rock and 12lbs of live rock + some crushed coral/coarse sand layered over with a bag of the finer live sand.

However, my question is about a sound coming from the tank ONLY at night. The best way to describe it would be 3 clicks/taps and a little shuffle of the gravel. It is definitely coming from the tank as I've literally stood over it while it makes the noise. It comes at irregular intervals, and is not the filter. Of course my suspicion is a little mantis shrimp, but crossing my fingers that maybe it's a pistol/snapping shrimp or something else. What do you think about the 3 consecutive clicks? It's ALWAYS 3 clicks.
Thanks

[jambon]

Sounds like a pistol shrimp... possible hitchhiker.

[Sailfish]

Yep, sounds like a pistol shrimp
Harmless, unless it gets too big (mostly only Tiger pistol shrimps).
As long as you are not losing livestock, I wouldn't worry about it.
Just make sure that your aquascape is securely placed on the bottom glass of your tank, so the pistol shrimp won't dig under your rocks and have them tumble down on top of corals or other live stock

[tam]

Are the sounds often followed with whooping noises? If so, that's a sure sign there's a Zoidberg in your system.