Mine does it also. It has something to do with the geolocation for routines I have setup when I arrive home and at other places. I’ve played around with it and if I turn the geolocation routines off it goes away.
also if I have the Amazon store app open it does the same thing until I close the app like it thinks I’m trying to talk to Alexa. If I hit the Siri button on the car twice it makes the audio go back to normal also.