Engine rattle

I have a rattling coming from the belt end of my 3.8 engine when idling. It is metallic in nature. No noise at higher speeds. I removed the belt and checked pulleys. The only questionable one was the idler. After replacing it the noise is still there. Not sure, but I think it is coming from the balancer area. Origininally suspected internal problems in the water pump, but I don't think that is it, either.
Is it possible that it is a #1 main bearing problem? Oil pressure is fine. Oil pump components? I will lift the car tomorrow for additional investigation.
Help??

The harmonic balancer is a possibility. The rubber does wear out and it will rattle. If you find that is the issue replace it as it can cause damage if it comes apart. This appears to be a common problem.

Thanks. The balancer does appear to be shot and makes a definative clank/clunk when the engine is stopped. I have ordered one from Texas. Only one I could find. They only had one and don't plan on getting anymore for a long time.

I hope that is my problem.

Just finished replacing the harmonic balancer.
That WAS the problem! Sounds great now. Rubber was totally disconnected. Did the job after being up for about 20 hours. Had me a little worried. Holding the flywheel gave me fits. Crank bolt had the original lock-tite on it. Ended up carefully using vise-grips. Worked great. Don't recommend it, though. I probably did it because nothing else worked and my brain was running on empty.
Anyway, another problem solved.