2010 Q5 braking noise

whats up guys. we have here a 2010 Q5 all-wheel drive. resently noticed a bang bang bang bang noise as the brake pedal is being pressed down to slow down. but when you press hard it goes away. so i was checking the pins in the caliper to be worn. but they wasnt worn. checked the metal reflex clip that keeps caliper in place to be ok. caliper mounting base is tightly secured. any ideas :banghead: