Over the last few weeks, I've noticed a slight braking noise on an intermittent basis, but yesterday it became a loud grinding noise. I dropped it off at the dealer (without an appointment) at noon Wednesday, and got it back 24 hours later. They replaced the brake sensors (see attached SIB) and brake pads (apparently a reformulated compound that's less prone to squeaks). And they gave me a Z4 loaner, which was perfect for the mid-70's weather that day! Once again, Peter Pan BMW (San Mateo, CA) comes through with great service!