mine rattles a lil too but i dont have a rear valence. many ppl have had this problem, i dont think the ww affects it. the piping hits something under car, like the heat shield or sumthing. i might have to change those rubber hangers or ghetto rig it somehow. somebody(i think larryd) stuck cardboard or a rag or sumthing under there
if it touched the rear valence just go buy one longer hanger at an auto store and put it on the hanger toward the tip(the last one).
should make it site a little lower so it wont touch the bumper.