Hmm.
I was at a restaurant in central Ohio a few hours ago and there was slight shaking taking place. I thought it was a small earthquake. Now I’m wonder if it was planes that could not be heard.
We not infrequently get helicopters around here with searchlights at night, but once several weeks ago there was a helicopter flying so low that it made our house shake. It was around 2 am and I was still up, so I had to go out and look, and darned if I couldn’t even see it. From the loudness, it was very low, though, and I could tell by using my head angle and both ears exactly where it had to be, but I would only see it when it caught the moonlight for a split second - and it was right over my head!
I was quite disconcerted, wondering who the heck would be flying a helicopter that low at night with no lights on - and how often that happened that I was unaware of! It was there for maybe a quarter hour, just circling around close by. Very strange.
Or blowing DUMBs.
I was actually in south central Ohio...a little east of Cincy a few hours ago, as well...there were 6 of us together for a very small, mini family reunion, and three of us felt something like that, as well. I kid you not.
Shaking without sound?