No, banging against the muffler had no effect.
I made a video of testing with steel tubes inside the tailpipes ( seems like Simon did the same).
You can hear me talking in German but it doesn't matter, I state the obvious: "noise is there" and "noise is gone", watch till the end, you can see that you don't even need the tubes.
I am sorry Rob, I see you live in Michigan, that is a bit far to take a quick look.