That was my first thought too.
If it is only doing it in SPORT mode and only when you let the gas off real quick, it is most likely the good ol' "pops and burbles" which are just part of SPORT mode - a kind of fun feedback that's engineered into the Cooper S.
If it is only doing it in SPORT mode and only when you let the gas off real quick, it is most likely the good ol' "pops and burbles" which are just part of SPORT mode - a kind of fun feedback that's engineered into the Cooper S.