Well, got the truck back today after its diagnosis... . and the answer, of course..... It is normal... The old wastebasket term for anything the customer says is wrong.
The said they put it on the diagnostic machine ( I asked if they had checked to see that the pressure delivery system was at specs and if they checked to see if it was a bad injector) and they said yes they had.
Furthermore they said that they pulled an 03 with 3000 miles and under load at idle created the same sound.
They said that the reason for the sound was that the MAP on a diesel, unlike gasoline engines, does not compensate for low speed air to fuel mixtures da da da da da.
I said, if we assume that this is the problem, that the diesel will show a knock at idle and especially at idle or low speed under load, then why would it have begun @ 9850 miles, and not been present at mile 1, mile 1000, mile 2000 etc.
They had no logical answer.
So their answer was not based on any symmetry with any kind of intelligent diagnostics.
In other words, it is normal
they all sound like this,
because diesels don't adjust for low idle fuel air mixtures properly,
but
in response to your question,
well then why did we not hear it until 9850, they have no verbal response.
We therefore assume that the unspoken response is the universal,
drivers are stupid, therefore the sound was there always, and they just decided to hear it now... or other blame it on the stupid driver syndrome.
The customer service guy said, we really don't want to tear down the engine, because you want to have it the way cummins put it together, and tearing it down could reduce its reliability...
Which means we couldn't put it together back the way we found it if we tried and we would have to either explain the left over parts or hide them.
Oh, well, as my good friend often said...
Matchless efficiency at every hand.
They do not have a clue, and are unashamed to report that the sound is normal in lieu of a solid reliable informed logical explanation.
I will drive this for another 1k or two and see what happens.
Thank you all for your help.
It feels so much less alone, with your verbal support.