In case you hadn't noticed, this community is SPAM FREE. Wonder why? Because it's actively maintained. If you're planning on posting anything non-automobile related, don't waste your time. We have 24 hour coverage.
If you are referring to the Nav unit talking over the radio, it is designed to do this. It is supposed to partially mute the radio so you are able to hear the "turn left at the next intersection" dialogue. You should be able to correct this situation by turning off the nav unit audio. It should be under "settings" for the nav unit.
If all else fails the owners manual should be able to point you in the right direction.