theres nothing wrong with your car other than the garbage audio system BMW installed at the factory.
http://www.e90post.com/forums/showthread.php?t=451762
unleash a professional on your car by dumping $1000-$2000 into it, and it'll sound just like, or better, than the $800 upgrade that those of us didnt get because we, like you, assumed the car would have a good radio. it does not.
btw, i love my new system.