My iphone 3 only partially connects to my 2011 BMW. No sound.

My iphone 3 pairs to my 2011 BMW and connects, but recently stopped sending the sound. It mainly worked fine for 3 years with it intermitently not picking up a call. It's not the car, I tested it with another iphone. I've reset everything repeatedly and updated the phone software.

Also, the phone works perfectly with my other car.

Any ideas? Thanks.