When the Falcon Heavy Tesla car reaches orbit around Mars would you be able to hear David Bowie playing on the car stereo?
(Assuming you could sit in the car during its orbit)
Sound requires a medium to travel through - like air or water. In space, there is no air (or other medium that sound could propagate through). Even if you could power the stereo somehow, you would not be able to generate sound with its speakers.
Also, it will not reach Mars orbit, it is on a free trajectory through the asteroid belt, almost to the same height as Ceres.
Yes, if you placed your helmet on the door frame (assuming the loudspeaker is placed in the door) and made sufficient contact to hear contact noise. The loudspeaker vibrates the whole door.
This assumes the stereo is still playing after all that time. The stereo (assuming maximum volume and 2x20 W of power draw) uses 1 kWh/day, so after 53 days it'll have drained the main battery. More likely, the stereo is connected to a separate 12V car battery with a capacity of less than 1 kWh, which will be empty in a day or so.
According to SpaceX, the Roadster hasn't been modified beyond the minimum needed to fit it on the payload adapter. That means both batteries are in place.