There's been some interesting chatter going on around the internet lately about mysterious in-game earthquakes happening throughout Azeroth. Seemingly at random the screen will shake back and forth for a few moments. There are no visible mobs or other occurrences that would cause this. However, these earthquakes are being reported by more and more people.
We know that Deathwing is going to tear Azeroth up in a big way. Take a look at the Cataclysm trailer for how destroyed the land is going to be. Barrens ripped in half, parts of Azeroth's climate will change, and general hell will come forth unto the plentiful lands. We also know that the world event ushering in the Cataclysm is going to be big, really big. The event itself is not in the patch files yet.
Or is it?
There are invisible mobs called Shakers in the game right now. There are two types of these mobs. The first is just called [DND] Shaker that was potentially in the game as early as patch 3.2.2, based on comments left on the live version of WoWHead. There was also another mob added in patch 3.3 called [DND] Shaker - Small.