Experiencing slowdown when I move the mouse

I am working on some particle effects, and I am experiencing noticeable slowdown anytime I move the mouse. I am not using any MouseEvents, and I even see this slowdown when the mouse is moving outside of the Flash window. Also, I only notice this slowdown when running the movie from within Flash CS3 (when I run the .swf externally, it runs flawlessly).

How can I make this slowdown disappear?