Clifton Jones

https://youtu.be/M46PpTjek6s Hey guys. Have a 2015 Silverado with 5.3 and stock exhaust except for the new flowmaster flow fx muffler. No exhaust leaks I can find. But it now sounds terrible with a raspy popping when you rev or let off the gas. I have no idea. Has the resonators, cats etc what is causing this and how do I fix it? Thanks for any help!