Kinda the same sound as a sonic boom maybe, but it seemed longer. Also much louder, as it shook all the windows like an earthquake, but no fan chains swaying to indicate one.
We had an earthquake near here a few years ago that woke us up in the middle of the night. At first it sounded like thunder from lightning striking just outside the house, then it rolled on for about twenty to twenty five seconds. It was loud, and low. Of course the quakes around here are small, and we’ve never felt one, not even that one, but it was the only one we’ve ever heard.