2004 350Z Engine Noise
 

I have a 2004 350z touring, auto trans, and it's got 195k miles on it. Very recently (week or two maybe), and only on cold starts, there's been a noise coming from the engine bay. Very short, but a kind of rattling noise. Maybe a second or two in duration. It wasn't loud and I started thinking it had always been there and for some reason I had never noticed it, and I attributed it to the age of the car. In the last two days, the noise has gotten much worse. Today it was very audible inside the vehicle and lasted about 5 seconds. The best way to describe it is a rattling, grinding noise. Car turns over just fine and the noise goes away after the 5 seconds, never to be heard from again until the next cold start. The car idles fine (no surging, sputtering, power loss, etc.) and the car drives fine (again, no surging, sputtering, backfires, power loss, etc.). I'm due for an oil change in about 1k miles. I change the oil about every 5k miles, give or take 100 miles, with Castrol full synthetic 5W-30, if I remember correctly. Any ideas on what the sound could be? Timing chain maybe? I'm gonna have my wife start the car tomorrow morning while I stand outside to see if I can get a better idea of the source, but as of right now, all I know is it's from the engine bay area.

Timing mechanism is officially worn out buddy.
In my experience; replace everything. You don’t want to have to come back anytime soon to revisit.