Find a tune on the radio.

You can unlock this achievement during the train based missions that take place between each main mission, 'Winter', 'Spring', 'Summer' and 'Autumn'.

On the Winter level you are told to find a signal as your objective and the signal for this is around half way through the tuner, however you can allegedly find a song at this point before finding the signal. I personally couldn't find one but it has been reported that you can. Otherwise, load up the Spring level and as soon as you gain control, turn around to see the radio on the desk behind you. Sit at the desk and tune it in until you hear music start to play and the achievement will unlock.