[DIYguy]

I totally agree with you.
You would think that the springs would do that.
But I can testify that they don't.
I suspected that the internal pivot point (the other end of the shaft) is where the rattle was really happening.
For that reason I added the hose clamps to force the shafts and butterfly plates inward against hard stops (after wiring them wide open).

It does indeed sound a little different, but is not objectionable.
Certainly better than the rattling/resonance noises.
And it cost less than $10 (for the clamps) and a few minutes' work to do.

But seriously, if I ever have the exhaust off for any reason I will properly eliminate them by one means or another.

Cat-back works too (as long as it remains legal in your locale).

[JT58]

My 2016 had a rattle at start up when cold, then it went away. I had to listen and listen to determine where it was coming from. I thought that it was one of shields or loose mounting nuts on them.. So I checked every one of them, nothing. I kept listening and I had thought that it was coming from the internals of the rear muffler. I was going to replace the monsterous muffler with an axle back anyway and finally settled on the MBRP axle back. No more rattle sound at all now with the MBRP on it. It was something in the stock muffler- broken weld, etc. deep inside. Nice to have that rattle gone.

[DIYguy]

Interesting as well.
Somewhere I saw a video of what is inside the OEM muffler.
There were a lot of baffles and fiddly things to go wrong.
But as I recall it was for a muffler with the motorized sound valves.
So I am not sure what would be inside of mine (base level, no motors).
Still, that is good information. Thanks.