Originally Posted by Corsairprime

I had a similar issue but not the same exhaust. AAM S-Line here. For me this turned out to be a clearance issue around the cross brace in the center of the underbody. A welded stainless piece of bar stock that secures the dual pipes together was vibrating against the brace. I grabbed some spare silicone tubing and wrapped the small stainless bar with it and secured it. My metallic noise abated.

You might check there. Hope this helps.