Sorry to resurrect an old post, but I just came across this and noticed there was no conclusion.
The 3.0 S/TDV6 has a small chain in each head to between the exhaust and inlet camshafts. When the oil pump becomes a little worn and the clearances get a little too large, the oil in the heads drain down back to the sump when the engine is switched off.
The rattle noise you hear upon initial start up is due to the two chains in the heads not having enough lubrication for the first few seconds. As soon as the oil pump has generated the oil pressure and pumped the engine oil up to the heads, the noise disappears as the chains and guides now have enough lubrication.
Always give the 3.0 a bit of time (say, 30 seconds) between start up and driving. This allows the oil pressure to get up and make sure everything is lubricated adequately before applying load to the engine. Kev
2014 L405 RR Vogue SE 4.4 SDV8 in Corris Grey
2010 L320 RRS HSE 3.0 TDV6 in Stornoway Grey
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