I've seen several AUX console jacks with loose-fitting female sockets. It sounds cheesy, but mess about with the cable and see if your SQ changes. Mine does but if I keep it in one spot I'm OK. It's a huge PITA to change, and I'm pretty sure they are all the same part. It's almost enough for me to switch to a USB thumb drive.
Musicar Northwest Portland OR musicarnw.com
High-performance audio for BMWs