I have run 2 cans of lubro Ml. diesel purge..which quieted it down some. Ran red line diesel additive with just a little bit of "new" diesel in a pitcher (like diesel purge) through the system which did nothing. I have changed the fuel filters under the hood twice now.

Today I put a set of injectors in the car which I pulled from a "junked" car with approx 250k on it (just like mine). These injectors didn't look as clean as the ones I had in the car, but I wanted to see what it would do and I found a place in Austin which will check the injectors free and rebuild for $20/each (so I can take the original injectors to them).

Surprisingly, the different injectors didn't appear to change the knock in any way except it sounds louder now on idle and quieter on take off.