Here in Texas, there is plenty of talk about an explosion on Columbia. This from the massive blast-like sound that shook houses all through east Texas.

As Tom mentions, it's clear there was material on Columbia which could've exploded. But the scale of the blast and the extreme velocity makes me think it was a change in Mach number or similar aerodynamic phenomea.

The think that really gets me is the atmosphere at 40 mi altitude is so rarified, (~.1% ATM at 20 miles feet!) that could it even conduct enough energy to be heard on the surface?

Is it possible this was a jet from somewhere scrambling to respond?