Or simply using a sensible amount of revs for the environment to not make it bark too much would work. I get annoyed with the valve systems I find and they are often much more expensive. When ever I have had a valved exhaust (last 3 cars have had a valved after market or Porsche sports exhaust which has it standard) I found without exception it goes straight into loud mode every time I start it. Even when I didnt on start up they are often just as loud for first few secs. I guess I may have a different attitude if I had neighbors to **** off but I also never seem to get above about 2.5k rpm in a supermarket car park as there are kids etc about.