It could be the cable. Each one of the bands on the miniplug represents a channel. If the plug doesn't make proper contact with the bands within your phone, or the bands within the aux port, you will get no sound. Try pulling the plug out a bit from your phone while the music is playing to see if it makes contact and you hear something. Worth a try.
2011 328i Convertible
: Mineral White; Oyster/Black Dakota Leather; Premium, Sport, Value; Sport Wheel w/paddles; Heated Front Seats; Satellite radio; HK Sound
2012 528i Sedan
: Titanium Silver; Oyster/Black Dakota Leather; Anthracite Wood; Comfort Access; Side & Top View Cameras; Cold Weather, Premium; Technology;
: Titanium Silver; Gray Leather; Premium, Sport; Fold Down Rear Seats; Xenon Headlights; Navigation System; HK Sound
2001 X5, 2009 528i