i can now confirm its there in my altis as well
i have changed the plugs and now i think it is there and can be felt when accelerating between 20-40km
at any constant speed between 20-40 there is no vibration only when u try to accelerate
most obvious if u have something lying on the passenger seat in a poly bag
the vibration can be seen as well as heard that way
alcapone has felt it in his GLI as well any body feeling this in XLI / GLI pl comment