jack up car, remove front wheeles, knock out pins from calipers, pull out pads, squeeze back pistons, use a small stiff brush to brush away brake dust, get a torch.....have alook where the top and bottom of pads sit and u will see sum metal pads/spacers that are bolted in. now listen a sec..... as you mostly use your brakes goin forward, discs turning towards front of car, so when pads grip they are forced down so dont touch bottom metal pad/spacer.... get a small screw driver and very slightly tap it under the top metal pad/spacer bending it down only about 1mm.....do the same for all 4 front pads, check pads still slip in/out easy, apply v.small amount of copper slip to top/bottom/back of pads and refit pads and pins and anti rattle spring, wheels on, PUMP BRAKES before moving off!!
what you have done is make the gap smaller so pads dont move so far and when they do they are cushioned by the bent metal pad/spacer......NO KNOCKING NOISE!!!!