Noisey engine on starting - 2003 RR 4.4

[hobbersinc]

When I start my 4.4lt Range Rover (2003 model) after it has been standing for some time (1 day or more), there is a rattling noise from the top end of the engine for circa 10 seconds, before it settles down to run properly. Does anyone have any thoughts on what might be the cause of this? I suspect lack of oil flow to a certain part of the engine - possibly the tappets, but what could be the cause / cure?
Cheers
Hobbersinc