<VV> engine noise

[Hugh Fowler]

It has been some time since Peg and owned our 1966 Corsa.  Our "new" 1965 140/4 makes a distinct tapping sound upon start up.  It goes away after a couple of miles of gentle driving.  I seem to remember some of this on our previous car but it would lead one to think that there is some adjustment needed.  The oil is at 3/4 of the full mark.  Is this oil just not getting to the right place at the right time?  Is it ok to replace the petro oil with Amsoil?  I have this in my other vehicles and have had great service.
Thanks
Hugh