Arbitrary Framerate Drops

I’ve recently noticed that my AS3 game occasionally stutters at around 20 second intervals. I lose about 30% of my frame rate for a few seconds. The problem is that my game cannot detect the framerate dips. My counter shows a perfect framerate, but is looks awful, and the fraps framerate counter shows a huge dip. Its almost like flash is rendering frames and then just… not displaying them.

The frequency of the stutters decreases as cpu load increases, intensity increases as cpu load increases. I’m 99% sure that the problem is not in my code, I’ve even started a brand new project with a Bitmap moving across the screen, it still does it.

Does anyone know whats going on?