Whenever we hear a crew member playing music aboard one of the Starfleet ships in the series (Enterprise or Voyager) it's usually something classical, jazz, or something else easy listening.
Does rock music or metal not exist anymore in the 24th century? Would this music be considered too 'violent' for human culture of the future? It would likely be something better suited to a Klingon's musical tastes.
We never hear a crew member mention "I'm listening to a band from the 20th century who called themselves The Rolling Stones" for example.
