Thanks everyone for your responses.
mk2, I think it's the tappets too but I am also going to check the manifold for extra vibrations. I believe the engine had been in storage for a year..Although I've already driven it for 50miles and thought that the good quality oil would help..
Maybe it's too thin for this engine but I don't see how that should be a problem as long as it reaches the lifters and lubricates them..and I have not seen the oil pressure light coming on.
I think the noise is not loud for 20-30 seconds after a cold start, and then it starts to rattle more audibly. I am going to double check that today.
Saw that. Cheers mate!