When the battery was disconnected for few days due to ML 350 (2004) engine service and then connected, the radio functions worked fine after entering the code, but there is no sound. It sounded that the radio is muted but the owner manual offer no clue how to get the sound back. It says to increase the volume from the on/off button on the top right of the system. Is anyone encountered a similar situation? I wonder if it is a matter computer programing.