There was a really loud noise behind me while I was stopped at the red light on North Avenue.
It was a helicopter Allegheny General Hospital. AHN LifeFlight (Allegheny Health Network)

“…..regional emergency helicopter and critical care ground transportation services for critically ill and injured patients who need immediate specialized care. LifeFlight is available 24 hours a day, seven days a week.”
In 2015 I posted -Grateful for MedFlightAir Ambulances in Columbus Ohio.