Sounds like a leak. I would check all the welds around the area or the clamps where everything is bolted together. It may not have been a quality job. If clamped together, just loosen the clamps and check that the pipes are firmly connected and the clamps securely tightened again. If welded, then look for cracks or holes in the welds. Should be a cheap enough job either way to have a muffler shop weld it all together for you. Hope you figure it out!
Thank you checked into all that everything’s good there. It happens once in a while it’s just been getting more often lately. The flapper valve is still there and almost sounds like the clicking/rattle comes from that .
Flapper is still there and that's kind of what I was thinking, but its weird that it only happens sometimes.
I’ve seen a few exhaust clips from shops on YouTube that have mentioned if replacing the muffler cut the flapper or it will rattle. Unless of course you have DFM active then you might get the helicopter sound without the flapper. Kind of a catch 22.
? Don’t have a great remedy either, besides a full new cat-back 
Thanks for the input going to cut it off this weekend hopefully that will do the trickI’ve seen a few exhaust clips from shops on YouTube that have mentioned if replacing the muffler cut the flapper or it will rattle. Unless of course you have DFM active then you might get the helicopter sound without the flapper. Kind of a catch 22.
Not sure what causes it, maybe the vibration of cutting the muffler in the first place loosens it somehow? Pressure gradient behind it with muffler gone
