AWE offers Resonated and Non - Resonated Downpipes. The Resonated Downpipes, which you're lookin' at, feature resonators larger than the stock units in order to produce a mellow sound volume. AWE strongly recommends the Resonated Downpipes for S - tronic cars when paired with the AWE Touring Edition Exhaust for ultimate sophistication and drone - control.AWE's optional Non - Resonated downpipes, are suited for owners seeking a loud and aggressive sounding system. Both our Resonated and Non - Resonated Downpipes feature larger than stock tubing diameter.These post - cat downpipes replace the factory resonated downpipes, and pair directly to existing AWE exhausts. They work with the factory exhaust, too, if you're looking to keep it stock in the back.Note In limited cases, the factory downpipes have been known to emit minor rattling noises when paired with the AWE S4 3.0T exhaust system. The possibility of rattling is eliminated with the addition of an AWE downpipe.