I believe there appears to be some confusion in this thread: with the NPP you have one of two settings as options in personalizing your preferences on your Stingray. You can have NPP set to "Auto" which means that the valves are controlled by (linked to) the Mode you have selected, ie: eco, tour, sport, track and each in turn controls the valves differently resulting in a audible difference between relatively quiet and authoritatively loud in combination of your current throttle position but dependent on the drive Mode. Or you can have NPP set to "Auto Off," which means the valves are set to be open at all times, resulting in an audible difference between relatively quiet and authoritatively loud solely dependent on your current throttle position independent (or regardless) of your drive Mode setting. I seriously doubt you can 'feel' the valves open or close but you can definitely hear the difference, and of course, if you are behind a Stingray at exhaust eye level, you can actually see the valves open or close.