On my 300D sedan, I am getting a nasty knocking noise from the engine.

sounds like "tang tang tang tang", like metal hitting metal. It increases in speed with engine speed.

Symptoms:

more apparent when the car is not fully warmed up.

only happens on take off, when engine is under load, but at low RPM. Once cruising over 40 mph, it goes away.

fuel injectors?
could a cracked prechamber make this happen?

chain stretch?