Parents have been concerned about their children's questionable taste in music since before the birth of rock and roll. At the dawn of the 20th century you could find adults complaining about the corrupting effects of jazz; somewhere there's probably been a parental complaint about how that newfangled Beethoven guy was too boisterous and loud. Remember that teenagers are learning how to differentiate themselves from their parents and assert their autonomy. Teens want you to trust them to make good decisions, even though they're still learning what that really means. Too much oversight in regard to their behavior will only cause resentment and rebellion. Choose your battles accordingly.
Compared to other worrisome activities such as sexting or underage drinking and smoking, listening to music of any sort is pretty innocuous in and of itself. Your teen's music choices may not reflect the values you want to instill in your child, and they may definitely not reflect your taste. But keep in mind that music is only one part of a complex puzzle that also includes television, movies, video games and other media input -- all of which have an effect in shaping your teenager's perceptions and values.
One area in which you do want to be aware of your teen's music is in regard to how she obtains it. Many teenagers swap music files in ways that violate copyright -- in other words, breaking the law. Usually they do this to save money, because an illegal copy means the music is free. For many teenagers this is standard operating procedure, but it's not only illegal -- it's not ethical. It's a lot like shoplifting. While it's rare these days, if your child is doing a lot of file-sharing, she can attract the attention of law enforcement. And if she's using your computer equipment to do it, you could be implicated too.
Even if your teen downloads all his music through completely legal channels, he may not be able to afford as much music as he wants. It's perfectly okay to impose budget limits on buying music. It's fine to insist he buy what he wants out of an allowance he must earn for himself, or from the wages of an outside job. Setting a budget with your teen encourages fiscal responsibility down the road toward adulthood and teaches valuable life skills.
Keep Communication Lines Open
Some studies have shown a link between extra-sexy song lyrics and early sexual activity, or misogynist lyrics and misogynist attitudes. Remember that correlation doesn't equal causation -- that is, the songs and lyrics aren't necessarily causing the behavior, or vice versa. The best way to deal with objectionable content in your teen's music is to keep communications lines open. Ask to hear what she's playing and talk about what you hear. You can express disagreement with the values professed in the lyrics without either condemning your teen for liking to listen to them or forbidding her to listen in the first place. Teach your teen to be a critical listener and to be media savvy. She'll be less likely to passively accept what she hears in her headphones that way. It's also perfectly okay to set a boundary about what she listens to within your hearing. Acknowledging that you can't control what your teen does on her own time is one thing. Having to listen to her blast music that offends your sensibilities -- or even just your eardrums -- is another.
Just as you want your teen to respect your limits, learn to be respectful of your teen's boundaries. Don't snoop in his music collection or secretly monitor his online activities. This simply destroys trust and creates an antagonistic relationship with your teenager -- the last thing you want. You're trying to foster an atmosphere of trust and support, after all. If you have concerns, talk to your teen directly.