Help with navigation voice

Does anyone know how to mute the radio when the navigation voice is announcing directions?? I listen to my radio quite loudly and it does not mute (nor lower) when the navigation voice announces directions. Its annoying. My old '11 Acura would lower the radio volume when it announced directions.

Thanks in advance for the help!!

2012 535i xDrive
White with Dakota Leather
All the bells and whistles!

Humm, mine does. Don't remember there being an I-drive setting for this, but there might be. Also, while the nav is talking, you can adjust its volume. Same thing with the phone. Once done, it remembers the setting.

Thank you!