I think I found a pic(s) of the factory 1M mid pipe resonator cut open. Like my German buddy told me... he sold his OE 1M mid pipe to a guy wanting a louder exhaust... so he cut open the resonator and was going to make a "straight pipe". But to his surprise... THAT is exactly what BMW had already done! So now we know why the stock exhaust drones a little bit!
Here are the pics I found on the web...
