Hello, I have a serious concern. From the boxes of my 451er comes for a few months shortly after you have driven some KM a seahhr loud deep hum and you don’t understand his own word anymore. The hum can’t be controlled by the volume on the radio. Only a turn off of the radio (Smart Radio 9) had achieved success so far or you had to wait about 3-5 minutes and it disappeared by itself. In the meantime I switched the original Radio 9 and the original Smart Boxes against a Kenwood DMX 7017 DABS and 2 new Boxes of AudioSystem, but no improvement in sight. The low frequency hum is still there, motor turn on, some KM driven and there it is for 3 – 5 minutes –> Ergo : on the radio and the Boxes it wasn’t defensively, and a high frequency LIMA whistle is not there either. Who has the same problem and could give a tip here, possibly a mass problem ? Am zt. vertlichratlos what it could be?