Eseries audio system failure

I had a similar issue with my Eseries. The sound quality went bad and then stopped. Does your USB audio or Bluetooth also not work? Have you tried testing the radio?

Yeah, the USB and Bluetooth are also dead. Radio silence across the board. How did you resolve it?

Given that the USB and Bluetooth are also non-functional, it sounds like a system-wide failure, perhaps not isolated to a single speaker. In my case, after methodical diagnostics including continuity tests of the wiring harness and a thorough evaluation of the amplifier module, it was determined that the integrated circuit responsible for audio processing had catastrophically failed. Considering the complexities involved, a consultation with a qualified automotive electronics technician is strongly advised to facilitate accurate fault isolation and subsequent component-level repair or replacement of the affected module. The repair cost was about 280€

Thanks for the info. I took it to a workshop, and it was indeed a defective speaker. Replaced it, and all is working again.