Where would those pieces you removed come from if not the cat? How would they get there if not from the core? Would they have not made noise and/or fallen out if they were there when you pull it out of the box? There are such things as manufacturing defects so it's possible the cat just happened to be flawed and failed after some use. It's possible you banged it on something, it doesn't take much. No matter, it's worth looking in to further because if everything is tight and properly gapped that's a prime suspect based on the pieces of the puzzle so far.

 

Go with a test pipe to see if the noise goes away.

 

Will you sell me your stock down pipe? Mine has a tear in the flexible piece.

 

First time I fit my 42dd dp i had it too high under the car and it rattled / buzzed against the heat shield

 

Okay, I'll be pulling the section off and looking at it again. However, I'm still getting the CEL from the rear O2 sensor. I've tried no spacer, 1 spacer, and 2 spacers, and still get the same code for the sensor.

 

What CEL are you getting? If it is P1114 "resistance too high" or P140 "no activity" or P1118 "B1 S2 open", you likely damaged the sensor when removing from the old pipe. I was very careful and still damaged mine. It was tough to get off, even with a 12" breaker bar so the extreme twisting damaged the internals. I replaced with the Bosch universal 4 wire and no more problems.

 

I can't remember the code, but it wasn't either of those. Does anyone have any experience with an O2 simulator? I'm thinking I may just go with one of those.