Microsoft Lumia 640 LTE, no audio when using GPS (Maps)

[Muse]

I didn't have this problem when using my 520, but since upgrading to the 640, I usually have no audio. Of course, driving a car it's dangerous to have to look at the screen of the 640 to figure out directions. I just want the audio, don't give a fig for the screen info. In fact, I usually lock the thing while navigating to save the energy use in lighting the screen. The navigation works anyway. But no audio? What could be wrong. I see nothing in Maps Settings. I opened Cortana and heard the female voice OK, although I never use Cortana. I still have my 520, although I don't have a plan for it, I can use it for GPS and I have it in the car. Still, it's an advantage to have data on while driving, presumably because the app can check for driving conditions. Comments? Thanks.