Can't remeber what aftermarket exhaust I bought for my Yamaha but it was called the silent stalker or something like that. Thought it would be perfect for hunting as the quad would be nice and quiet. YEA RIGHT! the thing sounds like a Harley coming through the woods!
After further investigation I was told by many sources that aftermarket exhaust systems are not quiet. You have to go with OEM. Maybe others have had better luck, but that is my experience.