Mr Kevlar

I just got done replacing my calipers, brake pads, rotors and guide pins for my front. Sometimes when I am coming to a stop, my brakes sound like a bus coming to a stop! You know that whining, noisy, grinding sound? The rotors look fine and I lubed all moving points where the calipers touch and the guide pins. Brakes work great, but this noise is driving me nuts! What else could be causing this noise?