KovacsC wrote:
I know the cars are designed to stop noise from the engine, but how can sound be stopped escaping though thin metal (speakers in the door) and single pane glass?
It's incredibly rare for your car to have bare metal to the outside - virtually every bit of it is covered in sound insulation:
Think about how loud a truck going by is when you're stood on the pavement, compared to how load it is when you overtake one on a motorway.
Or just get out of your car with the radio on, as suggested earlier.