I loved the initial sound when I fired her up the first time but was surprised on the drive home from the dealer as it was much louder than the stock exhaust. I can't attest to the 'fore and after decibel level but it was louder than I expected under acceleration. I thought oh, @#$%! What have I done!...but it grew on me and now that I've made it to 1,000 miles and have gunned it a bit...I too love the sound of the s/c and exhaust tone combined. At high speeds though--road, wind, and tire noise drone out the effect. There doesn't appear to be any excess vibration in the cabin and I don't notice any performance difference at low rpms...and I never did go past 3,500 during the break-in period so I can't compare at higher rpms. I assume there is less restriction and easier flow with less back pressure...if this adds up to more bhp or lbs/ft of torque than there is something extra I guess.