So, after not being able to find the funny plastic rattle under the hood, today it showed up when the timing belt wore a groove in the plastic cover and exposed itself. It has been trying for a couple days now. The belt, idler pulleys and water pump were replaced 5000 miles ago so I am guessing something is seriously mis aligned. I haven't torn it down yet but am wondering if anyone else has ever seen this.

 

Got an idler or tensioner pulley with a bent bracket? I don't know the V6 timing belt all that well, but all the pulleys MUST be straight & parallel with each other. Otherwise the belt walks off the pulley towards the engine or towards the platic cover... hhhmmmm??

 

OK, I just got through pulling it down, and like Jim said (pretty close) it was a tensioner pulley problem. The pulley is attached to the bracket with a nut and bolt. The nut had come loose, and finally backed completely off, letting the pulley flop all over the place.
The belt was really loose, but miraculously it didn't jump off so I really dodged a bullet on that one. I'll definitely locktite the new bolt.

 

Did you do the belt or take it to a shop? Think maybe they left it loose? If so, maybe they'll buy you a new cover.

You dodged a bullet all right. That's lucky with an interference engine. Make sure you verify the timing didn't jump 1 or 2 teeth.

 

Unfortunately, I did it myself. The tensioner pulley and bracket were new but I must have just installed it without checking to be sure everything was tight from the factory. My mistake! Since I don't drive the car a lot, it's been over a year since I did the job so I doubt I could get any warranty. Lesson learned.