This afternoon, I was doing the usual feeding and ferting of the tanks and fish. I have two very large 'fish bowls' with a Betta in each. One container is a large, tall glass column, the other a hurricane vase-large. Each have standard plants, Val, anacharis, water westeria, duck weed etc. I use plants that do not really need CO2. I change the water by 30 to 40% once a week, with natural sunlight as their source. As I was feeding the Bettas I thought that I heard what sounded like a far away smoke alarm going off every two seconds at the same raisng pitch. It was a faint sound but audible. Maybe is was a car alarm? No...My apt. is very quiet-very quiet. As I listened to this rythmic sound I noticed that it was actually being emitted from the tall column fish bowl. The Betta was at the top eating but the sound came from somewhere near the bottom of the column. I put my ear to the glass and sure enough!, that was where the odd noise came from. I got up and ferted the rest of my many tanks. The Anacharis. Jungle Val and crypt didn't move in the column neither did the fish. The sound had dropped in pitch and slowed a little. I had to go to work so I left. There were no bubbles seen, the snails were doing their thing and the Betta is alive and fine. What was that sound?? If anyone has a hypothosis, or answer to what could cause such an odd sound to come from an otherwise still body of water then I am listening. Thanks---R p.s. fish pictures are not my fish but added to show the type similar to my two.