So I just picked up a Magnaflow exhaust system (15267) and as much as I like Magnaflow, I was really bummed out to find that they have added a flapper valve to their newest model of this exhaust. I don't know who runs their R&D but the new version makes a ridiculous whirling noise when you give it more than half throttle. I just tuned my truck to correct the speedo, shift points and disable the DOD so this flapper is the last thing I needed.