458 Rattling noise from engine compartment 458 Spider

Way too hard to answer without an audio clip. Does it sound like an external rattle, like a piece of metal plastic tapping on something?
Or does it sound like an internal engine rattle, more like a knock?
Why does it take a few seconds to start? Is it because the idle comes down a little and the whole engine shakes a little causing the rattle?

I can tell you 2 common, and essentially "normal" (for this car) rattles/knocking noise that can cause concern is:
1- The exhaust flaps sometimes make a rattling noise when closed and car sits idling
2- There is a deep knocking rattle type noise when the car sits idling. It's very hard to locate, and almost sounds like it's coming from the front of the car (even though it's not) and it can be heard from far away as well. I'm not 100% sure what causes that noise, but I think it's caused by the EGR valve, and I hear it on all 458's. I usually hear it a minute or two after a cold start, at idle. Since you say that you hear the noise more inside the cabin, I don't think this is your noise, because I think it's much more pronounced outside, and in front of the car for some reason.

 

Could be the emmisions flush valves. Only about £50 a pair and very easy to replace yourself

https://www.ferrariparts.co.uk/part/ferrari/254425


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Also, wouldn't a defective flush valve cause a CEL?
P0441 I believe

 

I wonder if it's a belt tensioner pulley? It's hard to tell from the video, tough to hear a rattle noise. However, I think I hear a belt whine type of noise. I know that a pulley that is going bad, will make a rattle type of noise.
Did you sit in other peoples cars to compare? If it sounds like it may be right behind the seats, directly behind the firewall, it can be the pulley for the belt, or any accessory that the belt drives. It's almost impossible for us to diagnose over the internet, but we can throw ideas out blindly. If it was my car, I would put it on a lift (I'm lucky enough to have my own which obviously helps), and remove the belly pan. I would then run it and listen around underneath it. I think it may be obvious once you are under there.

 

I have the same noise in my 458, did you find it?

 

Have a similar sound too. Curious if there ever was resolution to this.