If the brakes are squealing, there's a good chance it is the brake pad wear sensor. A new design was implemented in January 2006 and can be identified by its green color.Google+
Car Problem Reports
BMW 650i New Brake Pad Wear Sensor Design Will Prevent Squealing
BMW 650i Problem
Average Mileage: 47,333 mi (20,000 mi - 71,000 mi)
Visitor, 2010 BMW 650i, 50,000 mi
Squeaking noise from brakes sounds like worn rotors. BMW advised it was how all performance brake systems sound even Rolld Royce.
Sound got worse after purchase, returned to dealer for repair. They replaced all 4 brake pads and front rotors. Noise continues.
I am returning to dealer. Looking for new car. Traded a 09 528i for this 2010 650 and have regretted every day.
Visitor, 2008 BMW 650i, 40,000 mi
Dealer tells me there's nothing wrong with brake squeaking---even when I don't have my foot on the brakes!!!! They are obviously covering up the real problem-the sensors!!! The car is beautiful but I have had NOTHING but trouble with it and have found other owners with the same problems, bad brakes and horrible transmissions. My car had to get a new transmission at 29000 miles and it is still no better. Yet the dealer insists nothing is wrong with the car???
Visitor, 2006 BMW 650i, 70,000 mi
I'm getting the squeal as well and told by the dealership that its attributed to the wear sensor and could be grinded down to stop the squealing for $100
not fixed yet what is average cost replace sensor and brake pads front only
Visitor, 2006 BMW 650i, 63,000 mi
my brakes squeal when i step on them, my mechanic can't seem to find the problem, even changed oem brake pads and still no use.
When in the parking garage or at a drive in... when you slowly apply the breaks... they squeak..