I have this problem too. I have discovered that the change occuring is the fade of my audio settings in Sync 3.4 is being adjusted when the Amazon app is opened. My normal settings for Fade and Balance is to have the listening center placed just in front of the rear seat in the center. The fade setting is changed when Amazon app is moved to the front of the car, so the only speakers playing are the ones in the front dash. When the Amazon app is closed, the settings get set back to my preference. I can go into the audio settings and move the settings back to where I prefer them. But, closing the Amazon app or bring it back to the focus of my phone, puts the audio settings back to where the fade is only playing on the front two speakers. I do not see audio settings in the Amazon section of Settings.