I have recently did a break job on my 2003 A6 quatro 3.0. Rotors looked fine so i didn't get new ones. The noise sounds like metal hitting against metal, when i hit any size bumps. At first I though that I forgot to putt the clips in on the outside of the break pads, but they were the when I checked. When i hit bups with my foot plented slitghly on the break pedal, there is absolutely no noise. I narrowed it down to being the pads, unless i am missing something. Are there more fastners that hold the break pad in place other than the rod like clips on the outside. What else can it be I took everything apart and cant find anything loose. The rattle itself sound like it would be the pads.

 

It could the dust plate behind the rotor. happens to everyone.
scarey at first. Just reach behind the wheel at push it away from the rotor.

otherwise try bleeding your brakes and see if that helps.