Try reseating the connector to the Head Unit.
Sometimes that works.
http://www.e90post.com/forums/showthread.php?t=1036190
Also try changing out the aux cable.
You need a plastic pry tool to get off the Radio trim .
Do not pry near the corners of the trim.
Its not necessary to dissconnect the climate controls
there is plenty of cable to put them to the side.
After that two phillips head screws .
The main connector has a lever which you throw to disconnect.