If the Jeep has an alarm system that includes vibration sensors, as some do/did, and if the choppers were very loud and “thumpy”, then it might have set up the alarm to go through the initial warning that would happen as it sensed movement. Not unlike if someone bumped the car while running by or something like that.
Of course! That makes sense. The chopper would create vibration. Well done!
I had a ‘92 Cherokee that chirped and flashed when someone sneezed.