The noise is random. When I try and look to locate it, I don't notice any fish out and about. As well, I don't have anything loose in the tank that can bang on the glass. Anything you know, or if you know of a site, anything would be appreciated. Pistol shrimp, like mantis shrimp, are stomatopods.
Stomatopods feed on small crustaceans, like hermits.
I think it is safe to say that there is a stompatopod in your tank. Once you capture it, then it is time to decide what to do with it. It's kind of fun to do the impossible. Well, I don't think so. Thanks for your response.