I guess it was probably back in the 1970’s when there were the booms off shore the east coast? A guy I knew was in the navy back them and told me they were dropping a-bomb depth charges on possible Soviet subs. I was young and half-way believed him. Now .....probably not? Those booms have been heard since colonial times. I don’t know if there are the methane deposits out that way - I wonder if they could be gas bubbles popping?
BIG BADA BOOM!