After a couple hours of lights out, something in my tank starts becoming very loud. I'm not sure if it's the filter, or one of the fish, or what. I'm not worried about it necessarily but it's a bit of a curious thing.
It sounds like someone pouring water in the tank. Not that gentle flow of water, but that loud bubbly gurgling kind. If that makes sense. I mean, in the dead silence of my house at night (it almost always happens when I'm about to go to sleep, so around 2am, long after lights out), especially since the tank is about 10 feet from my bed.
I never hear it during the day so I really don't think it's my filter, and the length of time for each sound occurrence is different. Sometimes it lasts less than a second, sometimes it drags on for ten seconds. When I hear it I usually rush over to the tank, but there's no water outside the tank, and it's pitch black so I can't really see inside it. I'm afraid to shine a flashlight for fear of startling everyone.
I have pearl gouramis, kuhli loaches, and harlequin rasboras.
Has anyone had something like this happen before?