Yesterday was the first ride with the bike since I had the tailpipe modified to quieten it down abit. It's is definitely quieter than stock and still has the stock appearance (no ugly downspout). I was riding with two other guys from HORRA, one of which also had an 06 400EXC. They both commented on how much quieter mine was. It's not a very scientific test as I have not had it measured with a sound meter and Cycle Improvements couldn't give me a definitive answer as to what the db was. I'm pleased with the result and would recommend anyone with a 400/450EXC to get this mod done. Bruno.