1. If there is no problem with the mobile phone playing music alone, and there is no problem with the DVD playback in the car and there is sound, there is no doubt that the problem is in the "Settings" part.

2. Check the music settings in detail, mainly the car part:

For example: whether the switching of CD, MP3, GPS navigation, etc. is switched to Bluetooth during playback;?

Is Bluetooth music turned on? It is turned off by default to avoid conflict with other sounds such as MP3 or navigation.

For some vehicles, such as your MP3 format, some vehicles are not compatible. It is generally recommended to use the standard MP3 compression format. . Of course, the A4’s original car-mounted equipment wouldn’t be so stupid.

Other possibilities are not ruled out.

The above content is for reference only. . Thanks. . .