interm. knocking noise at idle

[atomicpunk]

Hey guys, after driving and engine at proper temp. I hear an intermittant knocking type noise at idle, if I blip the throttle or rev anywhere past idle, the noise dissapears. It does not sound like lifter noise, or piston "slap". It seems to be coming from the top end, and have heard it could be anything from bad uim and or egr tube, to a failing harmonic balancer.
Any thoughts or experiences with this type noise?
Thanks, Brian

 

[melsg5]

those possibilites are all over the place, how about either an automotive stethescope or just a plain rubber hose to determine exactly where the noise is coming from.