This thread is teasing some old, old memories out of deep storage.
When i was a youngster our family would spend a coupla weeks at the beach on the Delaware coast. Maybe twice a week i'd hear a dull, toneless, directionelss thud, not too loud but noticeable in my estimation. Strangely, nobody else on the beach would seem to notice.
Since it was late 60s/early 70s, I am confident that the sounds were made by jets cavorting offshore and getting ready for duty elsewhere.
One fine morning I was up&at it rather early. I saw a lovely rollercoaster of exhaust smoke being laid nto the sky to the north. I got my parents to come look, just in time to see the sky artist coming down the beach in a Phantom going hell-bent for leather. He was maybe 500 feet up and a coupla thousand out, and for all the fury of his passage things were eerily silent. Until he pulled 20º past closest approach and then bboooomm. I asked my dad what happened. He explained in the language of our forebears (heh) that the plane had broken the sound wall. I spent the rest of the day combing the beach for invisible cinderblocks. cn