The game is particle effect happy so that may cause it for you. There are many areas where they just throw particle effects around, just to make that location more flashy. I am not talking about ability/spell effects, I'm specifically addressing background/environmental particle effects.
One of the main culprits I have experienced is the 2nd area on Nexus if you picked Exile faction and went to Northern Wildlands when leaving the ship (I think). It's the area that looks like a mix between the Barrens and Ashenvale. In the background there are flashy light blue lights going off all over the place and random ground effects.