a couple of things....
1. squeaking brakes that occur right after brakes are replaced is caused by a lazy-ass mechanic who doesn't apply lubricant to the back (yes, the back) of the brake pad fitting that slides into the caliper. it's rarely caused by the brake pad and rotor contact... but if it does, be sure you're following the correct break-in. i did a fully brembro install on an X5 and the recommended initial brake-in took me almost an hour of driving around and slowing (you don't want to stop fully with the pad engaged while you're performing the initial break-in of a warmed rotor).
2. your squeaky brakes (if they're not brand-spanking new) could be caused by a bunch of things. what i mentioned above is doubtful... it most likely is either dust buildup or a messed-up brake pad & rotor joining. try cleaning you rotors, and check your brake pads for wear. if that doesn't work.... any chance you feel any shimmying while braking, especially from high speeds? maybe you have some uneven wear or even warping that's causing your squealing.