I heard it the other day from afar. I came to investigate and saw a snail climbing the glass near an outlet. I dismissed it as it's shell on the glass. Then last night at 1245 am, the power went out. This was pretty much absolute silence besides my back up battery powering the reduced flow gyre pumps. Then the clicking started. Is it clicking or popping. Dang it was pretty loud. I hit the tank two or three times with a flashlight (no red) and didn't spot anything. I guess time will tell if it's a pistol,or a mantis. So far I haven't noticed any casualties. It's going on week 7 of the tank tomorrow. Grrrrr. I hope it's not a mantis. I got nailed by one back in the day. That was nasty.