Thanks for the reply, Barry.

When I listened with the stethoscope at cylinder 1 injector/prechamber area, I did not hear anything resembling that irregular knock. Maybe I'm listening at the wrong area... Should I put the stethoscope needle up to the lower part of the engine block around cylinder 1?

That knock is heard best from the cabin of the car, with doors and windows closed, especially when the engine is at its operating temperature. Trying to listen to the knock from the engine bay is a more challenging task, apparently. It isn't a "sharp" sort of noise - it sounds sort of muffled/obtuse, and diesel clatter inside the engine bay is really throwing me off from it right now. I'll poke around the engine block again... Maybe try to listen to the bottom end.

__________________
84 300SD - bought in April '06 with 237,000 mi