.... The signal transmission via AUX cable was unfortunately severely disrupted. I have my iPhone 6plus connected directly wired to the Radion ruled an error on the radio. Behold, the signal was clean. Thus, it was clear that noise came not from the radio, the iPhone ... but from the Freisprecheinrichtug itself. Unit back had.
I suspect that this is a question of a manufacturing error and a replacement unit would have worked super. Nevertheless, I think that's bad! I'm looking for another solution.
