Wow that is interesting. Mine is super smooth, so much that when I stop at a traffic light I sometimes need to check if start/stop turned the engine off. I cant really feel if the engine is running or not if there is enough background noise to block the engine noise. But maybe it is specific to some cars car/engines since in my case start stop also turns the engine on/off without any shaking, which is something a lot of people complain about. I agree that since it is a greatly mass produced engine that is also fairly complex, there likely is some variation among units.