[spielnicht]

That is a rod knock, usually caused by rod bearings going bad. Low oil pressure, no oil changes, and/or excess driving past safe RPM. Usually means the engine is done for because the at least one of the cylinder walls is now scorched and there is likely damage to the cylinder head. Worst case scenario - you'd also have a nice new opening in your block if the rod got thrown off of the shaft.

Sorry you're going through this. Went through it recently with a Mercedes and it wasn't pleasant.