2011 1500 with 4.7, I'm getting a rattle when I first start it and put it in reverse or drive. Rattle sounds like exhaust or heat sheild but not 100%. Park and neutral is fine. I got under it with my homemade stethoscope, the only thing making a rattle with the noise is the cat converters. But if my cats were bad, wouldnt that set off a CEL for the o2 sensors? I put a laser thermometer in front and behind the cats, hotter after but only by like 50°. Hotter after means working right. Idk?? Maybe it's not the cats??