I replaced O2 sensor 1 bank 1 after about 100 miles check engine light was back with exact code. Currently I am running a Ford Racing dual exhaust cat back. Driver's side is loose at the brackets in the rear. It rattles a little. Could that cause a problem with O2 sensors? What do I need to do next? I've heard of actually checking the cat, looking for an exhaust leak, and possibly cleaning the MAF (which is on a Ford Racing intake)? Anybody have some suggestions?