rattling noise at start up
I had the same problem on my 2012 370z. Nissan's responce was this: "I am very sure the noise your hearing is a normal cold start situation produced by the variable valve timming. The noise is caused due to the valve timming being advanced or retarded allowing what they call valve overlap.This allows the internal compression in the cylinders to be reduced for easier startups and for quicker warmups.As the engine runs the timming is returned to normal idle settings lessening the noise.
Typically the noise produced is a tinny sound though the tubular header type exaust manifold.If the manifolds were cast steel the performance and sound would be greatly reduced because of the exaust flow and sound dampening ability vs. steel tube header type manifold"
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