Wait, so you want to have a script where it plays a pre-recorded sound when something happens. Well, for a trigger volume, that isn't too hard.
( script startup al1
( sleep_until ( volume_test_objects alert_tvol1 ( players )) 15 )
( sound_impulse_start "the directory in which your alert .sound file is located goes here" none 1 )
)
For the script activating when Ai enters a vehicle is a bit harder.
( script startup al2
( sleep_until ( = ( vehicle_test_seat_list vehicle_name_here "jet_seat_name_here" ( ai_actors encounter_name )) true ))
( sound_impulse_start "the directory in which your alert .sound file is located goes here" none 1 )
)
I'm fairly sure the above will work.