2006 Vauxhall Combo rattle when cold startup

Recently bought a Combo van with 45k on clock & full service history.

Van generally very tidy but noticed on a cold start, that the engine rattles for approx 3-4 seconds afterwhich it goes away.

Generally I think that the engine idle is more noisy than I've been used to with my several previous VW Engines, but no unusual noise is heard as soon as rev's are lifted above idle. On the road it has lots of power & runs very sweetly.

Not familiar with Vauxhalls, so would somebody tell me who genuinely does know - is this normal??

ps: Thought this could be tappet adjustment needed & if so how difficult is it to do?

Thanks