WE have the same problem with our 335i. We had it also on our old 2007 4.8i X5 too.
We tool them to the dealer and the SA told me that BMW brakes squeal....Get used to it!
I wanted to choke him out, but instead, went over his head and talked to the Service Manager (who used to be a BMW mechanic and refreshingly was Sharp and didn't mind sharing his knowledge, which was Greatly Appreciated).
He scheduled the car to chamfer the pads and lube the stuff. He also tried some type of spray on the back of the pads to help with chatter or vibration. This stopped it for now.
He said that if it comes back, that he'll replace the pads with ones of my choice (I like Akebono pads because we've had good luck with them in the past and work as well or possibly better than OEM ones and give virtually Zero brake dust. Not too mention that they lasted over 55k miles on our last car). He also said that while he couldn't warranty the pads, he would still honor the rotor warranty.
That's someone who is willing to work with a customer to keep them happy! I was Impressed by him......................The Service Advisor, not so much!
