Grab a good heavy glove.....With the engine running...WARM...Place your gloved hand on the sheet metal shield on the turbo and see if this makes a difference in the noise......
I have seen these shields radiate a metric buttload of noise...
Easy to fix....Bolt on a strip of 1/4" flat lead to deaden the noise....
The injectors and the regular diesel rattle gets picked up and radiated by the shield.
My bet is a firm gloved hand on the heat shield will kill the noise....