Hi, i want an advice from you: my td5 defender (2004) have an horrible knocking sound at first 5-6 second from cold startup every morning.it's like a tumf tumf tumf, it comes out from bottom of the engine.
I'm using a Castrol diesel magnatec 5w-40 oil and this have 2000km on it, oil filter is new, and the level is ok.
What could be??

Does it make smoke from the exhaust when you start it up from cold?

If so, there's excess fuel getting into one or more cylinders.

Dodgy injector washer(s)?