Tap, tap, tap

[kien]

Originally Posted by nazerine

I would lean towards the snails making the noise. They do have defenses, which include raises and turning their shell rapidly .. and sometimes taps against the glass when doing it

My snails do this for fun. My hermit crabs do this too when they are running across the bottom of the tank close to the glass.

[danny zubot]

If you start to notice shells piling up in a certain area of your tank it would likely be a pistol shrimp. They like to collect building materials for their burrows. However, you have an orange spot goby which I believe could be symbiotic with pistols. So if you haven't actually seen the shrimp with the goby, you might not have one. Perhaps the snails theory is more sound.

[Aquaria]

Iv seen my snails do that as well mostly at night and it produces a tapping sound