The car has stood overnight, rattling sound any 1-2/10 sec when I start, what could it be ..?

 

Gonna need a LOT more info to even take a stab at it. Hard to diagnose rattles over the internet, you'd probably be better off going to a mechanic.

 

OK, thanks..

 

Johan, if you have a VQDE engine (2003 to 2005) this is not an uncommon problem and there is a TSB from Nissan explaining it. On a cold start one of the intake VTC (valve timing control) sprocket units can make a rattling sound for one second until it re-indexes. My 2004 did this every now and then for the ten years I owned it. I never bothered to replace it, as apparently it causes no long-term harm. I couldn’t find the 350Z TSB, but here is one for a Maxima that is similar.
http://maxima.theowensfamily.com/tsb/ntb03-060.pdf

This engine has a timing chain guide that tensioned by oil pressure, but it also incorporates a ratchet mechanism to keep it from losing tension when the engine is turned off. A problem with this unit will cause a more pronounced marble-in-a-can knocking sound that persists for longer than a few seconds at start-up.

 

Thanks Jennifer 2, that is exactly what happens during cold starts. Giant thanks for useful info ...