2 days ago on the way home I heard this terrible clatter noise from the car beside me at the light..........that car turned left when the light went green.......still heard the noise! Realized it was my car making the noise .

Ok, got it home and the clatter was coming from the serp. belt side of the engine. When engine revs the noise goes away. Took the belt off, started the car...NO noise. Turned all the pulleys and heard a slight rattle clatter from the steering pump....replaced the pump........still have the noise. Took belt off again....no noise. Turned everything that would turn and found nothing of concern. Put belt back on.....terrible clatter noise again....such that you can even feel the vibration of the clatter. Put my long handle screw diver on various components.....sound comes from water pump area. Could it be a bad water pump.....just replaced that last Aug.......don't hear any noise when I turn the pulley by hand........almost sounds like impeller is hitting the front of the timing cover? But then would'nt I hear or feel something when turning by hand?

Replaced timing chain/gears etc. last Aug. as well. If there was a broken/loose timing/cam gear it would make the noise all the time even w/ belt off?

ANY ideas?

My initial thoughts are the tensioner. Remove the belt and try to shift the tensioner up and down, and left to right.

It sounds like a bad bearing in the WP to me. When I changed my WP awhile ago, I experienced what sounded like marbles in the water pump. I guess mine was really bad because just before I changed it, it rattled at ALL engine speeds.

Did you have the AC going when the noise occurred?
You say it goes away when you rev the engine? If so my guess is the harmonic balancer pulley is bad.