It is actually illegal, but one of those difficult to prove in courts one, so is only usually done in crackdowns etc.
Public nuicence and all that. Should not be audiable from outside the vehicle.

As for noise on trains, it does not usually bother me, I usually have my iPod turned up full
Just kiddin, but I usually have it on, with noise cancelling headphones so cant hear it all. Just wish you could could get something that cancelled smells too!! I dont use public transport that much, but eeeeww its not nice in the summer.