Here is what the Rules Guy from Golf Magazine says:
Are there any rules about players listening to music on the course? I have a friend who does this, and it’s driving me nuts.” — Larry Meathe, Solon, Ohio
Not only is your friend annoying, he’s also in breach of the rules. Per Decision 14-3/17, a player has violated Rule 14-3— which pertains to artificial devices, unusual equipment or abnormal use of equipment—if he listens to music or a broadcast while making a stroke or for a prolonged period of time (as it might assist in his play). While driving from a putting green to the next tee? Permissible. Much longer than that? Penalties may loom—loss of hole in match play or two strokes in stroke play for the first breach; disqualification for the second. Your buddy may want to listen to the blues on the ride home.