Assuming you do have the sound file in the correct folder and are defining the resource correctly in description.ext. Then do the following
_soundobj = "logic" createvehicle [0,0,0]
_soundobj setPos getPos vehiclename
_soundobj say "whateveryouhavecalledyoursound"
Later do a
deleteVehicle _soundobj
The above assumes you are doing all this in a script. To do it in a trigger put this in the activation field:
soundobj = "logic" createvehicle [0,0,0];soundobj setPos getPos vehiclename;soundobj say "whateveryouhavecalledyoursound"
Then later have a trigger that has the following:
deleteVehicle soundobj
(Note the absence of an underscore if you are using a trigger)