I've been getting the same rattling since about 25k miles (car now has 58k on it). Starts intermittently around 3500 rpm, although sometimes less if the engine is loaded and i'm accelerating. I recently replaced the serp belt, and all the pulleys seemed fine. I was thinking that it could possibly be loose butterfly valves on the secondaries, and was going to take a look when I change the plugs out before winter.
-Chris
2000 SE Sport
