I'm not sure if there was ever a flapper valve, but there's not one there now. I covered the screens a few weeks later, probably a 15% additional increase in sound - worth it. I can notice a bit now when the engine kicks down to 6 or 4 cylinders - sounds like a Harley - but since this only happens when coasting, no big deal (I live in a mountainous area - always going up or down hill). As far as drone - quiet at speed, louder under load. Some back crackle when decelerating between 20 and 10mph (but I like the crackle). Have had trucks with aftermarket mufflers in the past with more drone.