No mention of cloud coverage at the time, but there are still a lot of unknowns about atmospheric phenomenon. Until we were able to do extended imaging of the atmosphere from above, no one knew about the "sprites", the electrical disturbances that extend upward out of the atmosphere. Since there have been numerous such unexplained "skyquakes" all around the globe for some number of years, I'd opt for an as yet unobserved natural source.

Back in the 90s I was sitting in an Alabama state prison tower late one quiet night.
For about four seconds I felt a gentle shaking and heard what sounded like distant thunder.
The next day on the news I learned that an abandoned coal mine in a named place that I knew to be near the prison had been dynamited to make it cave in.
Up until then I wondered if the Mississippi basin had "settled" again.
That was the reported cause of the same sort of shaking and distant noise heard when I was also sitting in a chair in an apartment during the 70s in a neighboring county.
And that was also at night.

Mythbusters filming episode on dry ice in a 2-liter coke bottle with little water?

Those booms are caused by Clemson players still scoring touchdowns against Oklahoma!

My wild guess is human-made but something ordinary, not secret or involving new technology.

My first thought was earthquakes like ones we had in WI a couple years ago: http://news.discovery.com/human/psycholo...
They're saying this appears not to be an from the ground.

I don't think it's a sonic boom because they said t was repeated, and a sonic boom is a wake of disturbance following an supersonic object. The places where it was heard were around 40 miles apart. I'd think it would be wider if it were a high-altitude supersonic aircraft. It will be interesting to find the source.

The timing between booms is sticking in my craw, though. I guess their regularity.

:-}

hahahaaahahaaaaaaahahaha

Okay. If you shay so. I agwee tooo.

I NonMooch... Snort

Yes. I have had an embarrassing misplaced keystroke in a heading before...

I ogree.

Yes.

Like meteor activity hitting the atmosphere?

Yesh

Natural.

Do you reeely think we neeed it???

Oh and I know how to spell Ok....I want an edit feature for posts!