Maybe someone had something similar and know what the problem?

 

I have a 2002 Lincoln Navigator 5.4l 4V. Mine also makes the same knocking noise when cold start. After the Engine warms up at normal operating temperature there is no more knocking noise. I have read somewhere there is a TSB that says it is normal for this type of engine to make knocking when cold however i could be mistaken hopefully someone on the tread can confirm or help point out why it does this.

 

This is due to the design of the pistons being so short. The pistons actually rock slightly and tap the cylinder walls each time they bottom out. After they warm up and expand the knocking goes way.