1999 Citroen Synergie diesel knock

Just bought this Synegie 1.9 Diesel and on a cold first start there is a terrible the best way I can describe it knocking rattling noise, which I have found improves once the vehicle warms up and gets up to the correct temp. I have had a mate check it from cold and he thinks it could be either the diesel pump is to advanced hence timing or one of the jets, any ideas girls and guys? Once warm there is a slight rattle which once you rev the vehicle does fade and then returns on allowing the vehicle to return to idle. Once driving it seems fine no real power lose typical turbo diesel really.