Unusual Noise from Engine

[OneTon4Fun]

My truck 2003 F350 6L 130K mi.
studs, egr delete, running innovative deisel tunes

There is a moderate to loud noise that I get at idle only. The sound is hard to explain, sort of like a buzz or growling sound. Happens hot or cold in any gear including park.

When you bearly pick up the revs (bearly touch the throttle) the sound goes away.

My truck runs fine and is fully capable of pulling my house!

I don't have guages nor does any warning lights come on.

Any ideas?

[Dirty_Stroke]

Possibly something loose and rattling, like a heat shield..?