Android Navigation install for Mercedes-Benz B C E V X GLC GLE GLS GLA CLA CLS 2016-2019 (NTG 5.0/5.1) cable connection & setting guide, android no sound /no audio fixed!
https://hifimaxgps.com/

NO SOUND Checking list:
(1) Check if you have moved the optical fiber cable correctly.
(notice the direction of optical cable, and you should plug to right spot)

(2) Check if you have connected the "USB/AUX "Audio box
(3) Check if you have set the "AUX position" correctly.
(4) When your phone connected to Apple Carplay (or Android Auto), it not allow to connect to OEM Bluetooth, if not, it also have sound problem.