Look up 'Seneca Guns'.
It's related to earth movement.
I live in north central PA
& have heard it several times in the last few years.
Here are a few links:
And a Facebook page for Seneca Guns in the southeast:
Kind of exciting when I read about it & realized that's what I had heard!
The next two times I recognized it right away.
One time it sounded just like an old time cannon.
Twice it sounded like metal scraping rock,
or two cars broad siding each other!
The first time it sounded like hubby was throwing wood,
into our metal wheel barrow, in the middle of the night!
It's a lot easier to recognize at night with less 'life noise'
going on or thinking at first it's something man made.
We live in a very quiet area, so noises get our attention right away!
I'm thinking the difference in the two types might be:
The booming is methane being forced out of a rupture,
or pressure snapping a rock formation.
The scraping sound could be one side of a fault line moving horizontally?
Did what you heard sound like a cannon?
edit on 27-10-2013 by wasobservingquietly because: Added links!