i just got my 04 ip coupe automatic with 51k miles, and i just notcied a weird rattle grinding noise which last about .5-1 second during a cold start. it only happens when i let the car sit for over 2 hours, but other than that it drives completely fine.i had my mechanic check it out before even purchasing the car and he said it looks good, no accidents or frame damaged. i just recently had an oil change, could that be a source? any ideas?

 

My car does the exact same thing, and so far nobody knows. Some VQ35DE experience this.

 

These motors are chain driven instead of belt driven. That's probably the noise you are hearing. It's completely normal and I wouldn't worry about it.