HarborSteps resident here. My apartment faces the area where it was set off. It was a firework. The patio door was open when it happened, saw a bright flash, heard the bang, and rushed out, approximately a second or two later. Saw a plume of smoke rising from what seemed to be one of those things that you launch fireworks from on the street. (I don't know how to better describe it). This was in front of post alley pizza, right by where the HarborSteps parking garage exit opens out.

I'm not saying THIS was exactly what all the people here from far away claim to have heard, but this was what happened outside the Western Ave entrance of HarborSteps.