Advice please, 2003 Alphard V6.  Recently had timing belt replaced, noticeably quieter engine afterwards. In past couple of weeks on cold start I can hear drumming noise, just briefly. Doesn't appear to happen on subsequent journeys. Could it be tappets? 

I don't think it has tappets, rather it has overhead cams. I think that perhaps it's VVT noise as oil pressure is rising.

 

Perhaps it's always been there and now you notice it because the background engine noise is reduced?

 

Anyway, if you have plenty of oil and no check engine or oil pressure lamps illuminated then I wouldn't lose any sleep about it.