I was not joking. A hard small crumb (like from pizza crust) can sometimes cause this. Look under/between the screen and the case at the edges where the screen meets the bezel.

You went from saying it was a "scrolling" problem in the first post to a "shaking" in the second post in the same thread. Those are different symptoms. Which is it, scrolling or shaking?

In addition to looking for something between the bezel and the screen, if that reveals nothing, was liquid ever spilled on the machine? Did it get rained on? Condensation?