I replaced my factory head unit with a Pioneer AVIC-Z120BT back in 2011. Honestly, I was satisfied with the sound. Of course, the OEM unit had really lowered the bar on that. But it started distorting badly, mainly bass sounds are coming from it and if you give it any volume at all it sounds like the speakers are about to self destruct. I just removed the Pioneer and plugged the OEM unit back in. Same thing. WTF? I'm searching for clues but if anyone could jump start the process by pointing me in the right direction I would appreciated it. Is there an amplifier AFTER the head unit that is maybe screwing up? My goal is just to get back to where I was before it started malfunctioning, unless that means giving Porsche two grand for some part.