My bimmer sounds louder now after over 2 weeks of driving with the valve open, I guess the left side of the exhaust has to break in a little if the valve was mostly closed before. It sounds the best when driving in a tunnel as the noise get amplified. Here is my bimmer and stock exhaust sound 800 - 3000 rpm rev. It also sounds much deeper when you are driving since the engine has to work harder.
http://www.youtube.com/watch?v=UXl-Ax5j0b8