Shaking Mac Screen

[bainbrig]

Any Mac users come across this strange one?

On my wife's Macbook, all of a sudden, after years of problem-free running, she has this fault:

On Safari (i.e. ONLY Safari, not Firefox etc), when she goes to Google (again ONLY Google), the first 4 letters she types makes the screen shake fairly violently.

Once she's onto the fifth letter, no shaking, and Google googles normally.

Not Google at fault, as it's fine on Firefox. Not Safari, as it's fine otherwise. It's a Safari+Google+first 4 letters (not spacebars!)

Can't delete Safari (OS component); tried deleting Google from Bookmarks, re-getting it from www.

No change.

Anyone come across anything similar?