Ahh finally hearing those mysterious boom noises that have been heard throughout the States.

Definitely without a doubt NOT thunder.

There was no distinct reverberation and it sounded as if it came from above ground.

It honestly sounded more like a train or some type of wheel moving over a cattle grid but of lower pitch. Not quite like that but that's how I would closely describe it. Maybe even a 12 wheeler with metal cage for cattle/sheep going over some kind of corrugated surface to cause vibrations in the betal but in a lower pitch.

2 booms. Second one much 'wimpy'er and sounded as if it had a weak 1 second start up before it got a bit louder but the resonance was still lacking and lacked the gusto of thunder.

Rural North-West NSW location.