2003 Grand Caravan 6cyl engine noise

[nipski6]

2003 Grand Caravan 6 cylinder with 25000 miles making noise at idle. Almost has the "rapping" sound like a diesel but not nearly as loud.
Anyone else have this problem and what could it be? Noise is not noticable at acceleration or cruising speed.

[nuts n bolts]

Yes I have heard the exact same noise. I mentioned this to the mechanic (deisel/knocking noise) and he said he heard nothing out of the ordinary. I only hear it when the hood is up, not when inside the vehicle.