[doreto]

Here you just idea/start of that you are asking for

pawn Код:

public OnPlayerStateChange(playerid, newstate, oldstate)
{
    if(oldstate == PLAYER_STATE_ONFOOT && newstate == PLAYER_STATE_DRIVER) // Player entered a vehicle as passanger (he is already enter it)
    {
        new rand = random(souce); // change 'source' wich your music list array or other thing that you have wich will random select one of them
        PlayAudioStreamForPlayer(playerid,rand,.......);
    }
    return 1;
}