Did you properly bed the brakes after you changed the pads? if not start there
also this
SUBJECT
Brake Squeal from Pad Wear Sensor
MODEL
E82, E88 (1 Series) up to 12/08
E90, E91, E92, E93 (3 Series) up to 12/08
E60, E61 (5 Series) up to 5/09
E63, E64 (6 Series) up to 5/09
E65, E66 (7 Series) up to 2/07
E70 (X5) up to 1/09
E71 (X6) up to 1/09
SITUATION
Depending on the driving conditions, the occasional brake squeak and/or squeal is normal. The conditions listed in this bulletin occurs during all light to moderate brake applications and is caused by contact between the brake pad wear sensor and the brake rotor/disc. This situation can occur on the front or rear axle brakes.
CAUSE
The geometry of the brake wear sensor, combined with individual driving habits, can result in a particular wear pattern which causes a squeaking and/or squealing noise whenever the brakes are applied with light to
moderate force.
CORRECTION
Road test the vehicle to determine the source of the noise. If the noise is coming from the brake system,inspect the brake pad wear sensor of the affected axle. If the sensor is in contact with the rotor/disc, remove the sensor and drive the vehicle.
If the noise is not eliminated, further diagnosis is required to determine the cause of the noise. If the noise is eliminated, replace the brake pads and wear sensor of the affected axle.