From the clip it sounds like the timing chain?

 

I'm inclined to think so too - try and get someone to record you start it while they're standing over the engine with the hood up so we can get a better listen to it. Let it idle for 20-30 secs and keep recording too

 

Yeah, you cut the video way too short...

 

 

How many miles on the car?

 

Don't know these engines myself too well, but too me is sounding like an external (outside the engine) noise... maybe a bad pulley!?
I mean I hope for you...

To more experienced people out here... do these engines have a hydraulic chain tensioner?

 

Yep, two of 'em, one on each bank.
Quote from page 56 of the AJ133 Technical Training doc:
"Each camshaft chain has a spring-assisted hydraulic tensioner operated by engine oil pressure. The chain tensioners also incorporate a ratchet mechanism to eliminate start-up noise. The chains are lubricated via oil squirt tubes located at the front of the engine block. Nylon chain guides control chain motion on the drive side."
Get yourself a copy of this doc from my Dropbox here: https://www.dropbox.com/s/8y4iax9hm2...%20V8.pdf?dl=0
Wear on those tensioners and their guides is a common and well known problem, when worn they rattle quite a lot, a few threads/posts around here on the topic. Here's one: https://www.jaguarforums.com/forum/x...-techs-159928/

 

@OzXFR - Thanks for that document!

@hen555 - That might be your issue then!? Reading trough the thread that OzXFR posted, kind of hints to that.
That ain't a cheap fix that's for sure... do you know any good mechanic that could help with diagnosing this and help you fix it?