This is weird though... for a non-nav car with the Hi-fi amp, the Android unit should play nicely. My Avin 2 worked perfectly fine in my old nav equipped Hi-fi sound system. Didn't run a single speaker wire or remove the factory amplifier. Sounded great.

It sounds like you are going to have to pull everything to see where the installer messed up. If everything is plugged in at the dash using the correct harness... you should have no issues AFAIK.

EDIT: How was the audio quality pre-Android unit? Any distortion present?

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)