Noisy engine on tickover

[malcf]

Just got the wife a replacement car a Megane cc 2litre vvt 136 and have just noticed that the engine is noisy on tickover sounds a bit like a diesel but only when warmed up,as soon as i rev it it goes quiet and when its just started and cold it is quiet,i am thinking it could do with an oil change was thinking about fully synthetic 10/40 has anybody any thoughts on this?.