When I place a phone call with the radio on the radio is automatically muted so I only hear the phone call. But when I have the radio and navigation on at the same time the radio is not muted when the navigation voice speaks. It does sound like the radio volume goes down a bit but is not muted which sometimes makes it difficult to hear what the navigation voice is saying. Is anyone else experiencing this? Is it normal? Is there some setting I'm missing that will cause the radio to be muted when the nav speaks?