Guys need your help,

I got a 03 Sedan with Coupe Midpipe and Stock Muffler. Just finished installing a HR Y PIPE.
I now have some rattling noise coming from somewhere underneath. I figure it's gotta be the HR Pipe becuase I never had rattling before with my de pipe or midpipe.
Sometimes when going over bumps you can hear it rattle (like up and down or). When turning or going slow mostly that's when u can hear it. Going fast going over speed bumps you can't.
It's driving me crazy.

I haven't had rattling noise before, but I don't think it's the heat shield, because I pulled out a bunch of rusted heat shield when taking off my DE Pipe.

I put on new gaskets but reused the flange bolt hardware. It seems pretty tight.

I cant' figure out what the rattling noise can be, I'm thinking about taking a ride to the mexican muffler shop.

Any ideas what it could be?