[miokie]

Get the vehicle the main player is driving:

Code:

new VehID = GetPlayerVehicleID(playerid);

Check who else is in the car that isn't the driver:

Code:

for(new i = 0; i < GetMaxPlayers(); i++ )
{
if(GetPlayerVehicleID(i) == VehID && GetPlayerVehicleSeat(i) != 0)

Play them the audio.

Code:

Audio_Play(i,audioid, pause, loop, downmix);

So to conclude:

Code:

new VehID = GetPlayerVehicleID(playerid);
for(new i = 0; i < GetMaxPlayers(); i++ )
{
    if(GetPlayerVehicleID(i) == VehID && GetPlayerVehicleSeat(i) != 0)
    {
        Audio_Play(i,audioid, pause, loop, downmix);
    }
}

That will play the audio to everybody but the driver that's in that vehicle.