Look at the thread on the link below. After working in exhaust for over 2 decades I can be almost certain that the picture the guy posted was not of a Borla muffler, but the picture of a cheaply manufactured header/manifold merge collector. On all Borla you can see the perforations of the cores, they are perforated entirely, not solid on the ends. In the picture you posted, there are no perforations, but solid tubing, that seems to curve instead of going straight as a muffler should do.
I do agree with you, they need to correct the design or come forward with an explanation. This is the same thing that happened with the Dynomax VT a few years back. It was a great muffler, no drone at all while cruising, but the flapper clanking on deceleration was annoying to the point that customers wanted them off, since Dynomax offered a lifetime limited warranty on them.
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The guy on Vortex that posted this image said it was a Borla system. I guess he could have been wrong.
Great info, though. Thanks for sharing.