Pbondar said:
It may be something to do with analog signal levels..BMW specialises in weird signal levels..3 ish volts on signal wiring..
Yeah, I'm all for good sound and I'm sure the AUX is by far the worst possible way, but when you're doing 70mph down the motorway with the roof down you ain't hearing the quality sounds anyway
Even with the roof up, tyre noise, engine noise etc, nobody will notice the difference between the CD quality and the AUX input.
Whereas is it truly is bad audio then a good point to start would be some electrical cleaner in the AUX socket as if it hasn't been used much (if at all) then it could be corroded! Now this would have a very bad effect on sound quality.