my first thoughts would be a rod or main knocking.


you can try to isolate any external parts like the alternator or anything else driven outside the engine by disconnecting it, removing belts etc and run the engine to see if the knock persists.
there also is a tool you can get called a stethoscope (for technicians) that has a needle on the end of it and listen to different parts of the engine to see if you can locate the source that way.

try cracking the injector lines while running and listen for the most noticable change and that may tell you if it is a rod knocking and which cylinder it is on.

other than that i'm not sure what else to tell you other than tearing the engine apart and looking for damaged parts, bearings etc.