Originally Posted by ImportConvert

Berk CBE is sounding good. However, I noted resonance at 3700rpm under 3/4 throttle in 2nd and 3rd and 4th gears.

A bit of trial/error brought to my attention that it was the glove box, specifically, the huge fat stack of owner's manuals and tire-lock in it. I removed them to the compartment behind the passenger's seat, and the issue is gone. It now pulls through the revs as far as I am taking it at this point of break-in without any vibration. It's a nice exhaust, does what I want, and looks great. Car felt a bit peppier after installation.