Only happens at a certain speed and gas pedal position. Sounds like heat shield but I can only replicate it at about 55mph when I am trying to maintain that speed. Muffler shop said they did not see anything loose but could be inside of muffler. They also said it sounds like I may have a small exhaust leak on passenger side but they do not mess with that far up. Only from flange back. Sounds like it is the CAT as it is right below my feet.

I did a search and found one person had a crack and another had a heat shield issue. Anyone else?