I recently turned on my bmw 2008 550i and took it out for a spin and when i brake on a 50mph speed it sounds like a grinding noise in the rear.
My car has 90000 miles.
My car has an automatic transmission.
Grinding, squealing, or other "noise" on braking is usually related to a brake pad/rotor contact problem. These surfaces "mate" when you apply the brakes and if there is scoring on the rotor, rust, dirt, irregular wear on pad or rotor, wear-out (no pad friction material left) or any of a myriad other defects and imperfections you can get noise. The most efficient thing to do is request a noise on braking diagnostic during which the responding certified mechanic will physically inspect the brakes, as well as road test the vehicle, and give you a conclusive finding as to what the source of the noise is and what the cost to eliminate it will be. If you have further concerns, please don’t hesitate to follow up.