Like Rick asked, better or worse when hot or cold? Can you see any signs of carbon around any of the flanges? These kinds of sounds are usually from some type of exhaust leak.
Best to break down and take your baby into the dealer, instist on taking the service writer or the mechanic for a ride so they can hear it and let them know (tactfully) that you expect them to fix it. I go so much as to tip generously, even if it is warranty service. My service people love me and my truck and have bent over to do things for me and ignore the changes that I have made to Moncha.