Wow! Not hard to find it!

http://www.youtube.com/watch?v=VvnHyU8e1c8

But, here is a video from a guy who has info from a local airport that says it was a huge Fed Ex jet engine being run at exactly that time. huh.

http://www.youtube.com/watch?v=behlPRwsmrc

As I said, we had that kind of sound all the time growing up just about 10 miles from a Navy base, so I can see how it could be just that. The sound is tricky too, I think, depending on the weather, it 'bounces' off clouds or something, because it would be a low rumble sometimes, and others it would sound like something was flying/hovering right over you, it was so constant and loud (vibrating).

Just my two cents.

Blessings~

Suzi