Problem with multiple displays
I just upgraded to Mountain Lion on my MacBook Pro (15", Intel i7, ca 2010) I think from Snow Leopard, and now I am interrupted at least once an hour with a weird display issue. It's hooked up to an external monitor (Apple), and for about a minute I have no cursor or keyboard functionality and the screens will shift slightly left or right, kind of like a slow tremor. It's annoying and it interrupts my workflow. What is going on? This never happened before I upgraded to Mountain Lion and only happens when I'm connected to an external display. There are no recent updates showing up in my App Store icon so the OS should be all up-to-date.
MacBook Pro, OS X Mountain Lion (10.8.2)