[Antec800]

Alright so I’m not sure if this is a characteristic of the crappy rear muffler of my 17 340i but Once I installed a ctless dp the rear muffler has a metallic buzz when I rev or drive, regardless if the valve is open or not although worse when the valve is closed. I’ve installed a bigger 12 in dynamic resonator in place of the stock resonator it made it a little better but still bad. Has anyone cut open the stock rear muffler and found loose parts or metal in it?

[Wires]

I doubt it's the muffler, it's more that either your DP is rubbing on the frame, or your mid-pipe is rubbing on the cross member.

[kern417]

Or you're just hearing the notorious flap rattle. Sometimes I could hear mine even when my exhaust was completely stock.

[Antec800]

Nothing is rubbing took it to a exhaust shop to make sure, and I kept the flap open and unplugged it can it still make that noise?