Try swapping the pads side to side on the vehicle. Squealing is often caused by uneven wear of the pads. By swapping the pads roundyou reverse the wear problem. This is what those small anti squeal shims do, they wedge up only half of the pad to make that bit touch first. A bit like setting up push bike brakes so the trailing edge touches first pulling the rest of the pad on, where if the leading edge touches first it drags itself along the rim or disk forcing the rest of the pad off, the repeated grabbing/dragging and release it what is squealing.
Off course some combinations of pad compound and rotor are just noisy, but usually thats a kind of grinding/rumble not a squeal.