1. Install Audi-A2DP in your car
2. Setup Bluetooth Settings on your phone
3. Optimize Audio
For better audio quality, the Auxiliary (volume) input level in MMI should be set to maximum. To do this, go to Media > Source > External Audio Input > Setup > Aux Input Level.
In addition, the volume should be amplified closer to the audio source. To do this, set the MMI volume to low. On your Bluetooth device, set the volume to near-maximum. Finally, gradually increase the MMI volume to a comfortable level.