a tech2 or tech2win (pc software/obd interface) would do it for sure, not sure if other scanners would do it or notNo, the noise also comes when the plug is bridged. It doesn't matter which channel is set on the radio. The front speakers work perfectly, but the sound from the rear is very quiet and the loud noise comes from all rear speakers.
what kind of tester do I need? Unfortunately, there is no information about this in Germany