Brake grinding with brand new brakes can be caused by several issues. First, your brakes may have changed to semi-metallic discs and calipers and they may be wearing in. Second, you may have hit your new semi-metallic brakes a bit hard during the run-in process so that you have created glassy areas that have to be cleaned up. Third, you may simply have a mismatch between brake materials. The rotors installed may have called for a specific kind of caliper or a caliper material that does not match. It might be something as simple as a problem with the brake-proportioning valve. The solution, though, is a visit to the repair shop.
For more info, see How to Understand and Diagnose Common Brake Noise