I own an Automatic 08 G37s Coupe with Tanabe axle back, Berk HFCs, HPS Intake Hose, and K&N drop in filters. A few weeks ago the catalytic converters started to give out and I started to hear a noise coming from the left side of the passenger's seat. It sounds like a tiny piece of metal spinning around in the exhaust. I ended up having the stock catalytic converters replaced with Berk HFCs and it only made the sound louder. I have tried to poke around the heat shield but it doesn't seem to be loose. I am thinking that some pieces of the catalytic converter maybe got trapped in the Y pipe but I am not too sure. I would love to hear what your guys' opinions.

Sound Clip
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Sound clip taken from the left side of the passenger's seat. Windows up.