[BOBL]

The oil pressure will sometimes take a few seconds after start to register best pressure.

The rattle is not because of the oil pressure. It's because the engine is a diesal and that's the sound of small diesal engines at low rpm..

 

[BOBL]

I think he means he hears a "dry knock" because if whatever sound he's hearing goes away once the oil light goes out, it's certainly not normal diesel clatter he's referring to.

I agree, but I would feel that an engine knocking (piston slap, wrist pins, etc.), would have given up by now. If it's not low rpm rattle then it's time to see the dealer.

 

[BOBL]

OP,
I have to ask who manufactures the oil filter you are using . Good oil filters are designed with a valve in them to prevent the oil from draining back into the engine oil pan. If you are using an off brand filter, or maybe a filter that is cheaply made without the back flow preventer, this may be your problem. I timed my startup yesterday and my oil light goes off in two (2) seconds. However that doesn't eliminate the "normal" diesal rattle. Time to change your oil and move to an OEM filter.