Just noise control.
Now that I think about it, the flap is vacuum controlled. So, just make sure not to create a vacuum leak -- seal up the hose end tightly. I recall that many people use a golf tee. Google golf tee mod BMW, and you will see that this is very common either to leave the flap always open on the stock exhaust, or when installing aftermarket exhausts.
__________________ Turkey Fleet Bond Holder
Originally Posted by BMWBeauty416
I'm scared if you took pictures of me cleaning a rifle Dave might consider it porn