I had never heard of the exhaust valves until recently. My F is in Spain and got an advisory re noise. It has a standard cat and MS back box so not really considered loud. I have seen on ebay sound reducing valves, do they work, or can some one recommend something.
The problem with sound reducing valves is that they need a very invasive work on the exhaust tips, cutting them, soldering the plates and fitting the valve.
The way our exhausts are designed (diagonal tubes), it would be VERY difficult to precisely cut the tip and fit the valve without altering the position of the tip in the rear bumper. It's something that needs to be done with precision cutting tools and millimeter-exact positioning of the pieces before soldering, i.e. something that falls outside the usual DIY tools/skills