i hear ya crabby. i was skeptical too until i actually put my ear to the bowl. originally i thought it was the TV or cable box or something. it can't be the filter since it lives in just a fish bowl (no filter, etc.) and before anyone says that bettas would be better off in a filtered tank...i know....but that isn't the point of this post so please spare me. it DOES live with and african dwarf frog that stays at the bottom of the tank. i've ruled out it being the frog since he is on the bottom of the tank, i doubt he would make such a loud noise. the betta sits at the top of the tank all day, barely moving, so i think the noise must be coming from him. i used to have him at work but he was so damn boring, i brought him home and brought my female betta to work since she actually has a personality. He never made this noise when at work. the noise is so loud that i can actually hear it over the tv. it's weird.