Kavod HaRav, if one gets into their parent's car and hears them listening to secular music, can one ask them to turn it off or is it not Kibud Av Ve'Em?

Few points:
If someone is violating the Torah you should rebuke.
You’re only allowed to rebuke if the person has a close relationship with you so he will listen.
Parents must be spoken with much respect even when rebuked it must be done in a way that doesn’t sound like rebuke.
No need to rebuke over music.