Turns out SpaceX over in McGregor was conducting a full-burn test of its Falcon 9 rocket — all 9 engines, burning for the three minutes it would take to get to orbit. Normally this wouldn't be audible all the from Waco — or at least, not that audible — but the atmospheric conditions turned out to be just right. (Here's the official SpaceX video of the test.)
I thought it was way cool — but as you can see from the comments at the links a lot of people didn't, and are theorizing that SpaceX not knowing the sound would carry that far means Something Went Wrong And The Coverup Has Started. Talk of lawsuits is flying (I don't know yet how serious, or how far it could get) and the NIMBY Brigade is out in force. I'm hoping it doesn't get far enough to get the McGregor facility shut down — Falcon 9 in particular is our only non-Soyuz ticket to the space station once the shuttles are retired and until NASA's Constellation system comes online, if it ever does.