Hi all, I had some exhaust work done to my 2007 G35x a little while ago, due to some rusted flanges and so on. The shop ended up making a dual system from the cats back with an h-pipe between each bank. Mid-pipes are stock, and mufflers were replaced with a magnaflow style muffler. It sound great aside from the little issue below!

Long story short, I've noticed a fluttery noise that is mainly heard from behind the car when revving. I'm quite sure I get the same noise audible in the cabin when accelerating between 2k-4k as well. Almost sounds like a manifold leak. But when stopped I can really only hear the noise from the tail pipes.
This would lead me to think its being caused by turbulence or something loose inside the exhaust as opposed to a leak, with my first guess being the insides of the catalytic converters are loose and are rattling around, but I can't be sure.

I filmed revving the car from 3 different places, behind the car, under the driver-side cat, and under the axleback/midpipe connection. Again, I can really only hear it behind the car, when revving from idle, and as the revs return to idle.

Curious if anyone has heard a similar noise and can confirm/deny my hunch that the cats are the culprit.

Thanks!

 

First part of the video sounds like an exhaust leak. Smoke test the exhaust to see if it's actually sealed up right.