At 65K miles, I replaced the idler rollers for the serpentine belt this weekend. They were making a rattling noise like something was loose in there. The bearings had some play in them that was causing the rattle. Sweet silence now.
Several folks have talked about their bearings exploding and causing damage to other parts so you may want to look at replacing them as the mileage adds up. The parts were $150 from Sunset Porsche ($300 at the local dealer) for all three rollers and the hardware that comes with them. It took about an hour, with about 20 minutes of the time spent opening/closing the front engine cover. Only 4 sockets needed and one open-end wrench. I'll post the procedure on my website soon if anyone wants to do it.
As an aside, I'm going to pull one of the rollers apart and see if the bearings can be replaced with some higher grade bearings that may last longer and cost even less.