Need help with mystery noise

[russp]

A very small pistol can make a very big noise , I was running a canister filter when I first started my tank & one day when cleaning the filter I came across a pistol shrimp that was about 3/8 -1/2 of an inch . I put him in a 10gal that I have set up & ever since the snapping started in that tank too , & it is loud enough to be heard all through the house at night. Also turbo snails can make a very similar noise by spinning there shells back & forth quickly & hitting the glass . I have witnessed this a number of times.

[asylumdown]

Mystery solved!

During the day, my turbo snails cluster against the glass beside the heater in the corner where it's shaded. I was finally looking right at one when it puffed it's shell far away from it's body and started spinning it rapidly. Now that I know to watch, I've seen them do it a couple of times. When the shell only knocks against other snails (Is it a territorial thing?), it makes a softer, more muted noise. When it's right against the glass, the knocking sounds like the tank is about to bust open.

It sounds like the sounds is coming from 2 feet from where the snails are making the noise. Acoustics are nuts.