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It's certainly worth further investigation. I would remove the oil filler cap and see if the noise is coming from inside the cover and use a wooden rod or similar as a listening rod to see if you can identify the location a little more precisely such as the VVT solenoid, if that is external. If removing the filler cap shows the rattling to be coming from inside, then remove the cover and do further checks.
If you suspect the tensioners then you shouldn't even be starting the engine to listen to it. Take one of the cam covers off and see what generation is fitted and what state they are in. It's very easy to change the secondary tensioners as a precaution:-
Shortly after buying my XK8 I noticed a noise after revving the engine, which induced a mild panic. But In that case on close inspection with the help of a friendly local Jag specialist the sound was coming from the area of the cat rather than the 'top' of the engine and it turned out it was the Cat breaking up.
Pulled valve cover and found my June 2001 engine had been refitted with third generation tensioners. Removed VVT solenoid to check. Looks like missing an o-ring. Guessing this could cause ticking by oil leaking past where the o-ring should be.
Despite finding out I had third generations tensioners, decide to pull oil pan just to check for any debris. Totally clean. Checked oil pump pick up screen and also clean. FYI, you can remove oil pan without removing under engine X-brace.
Next up is transgo pressure regulator retro fit, filter change and home transmission flush.