Hi. and thanks.
It's a jauger gauge. Have pressure of 25 idle/near 60 at 2000 revs, even on very hot days, so that seems good.
It does rattle on start up, even later in the day a bit sometimes (have a Mann filter, tilted downwards).
As it has apparently good pressure, then maybe, ignore, as some very knowledgeable/experienced folk have suggested, or could one or two bearings be suffering.
No facilities to remove engine and work on it, So could maybe? remove Sump (Vitesse) in situ and replace shells, though prefer not to if it's likely not a issue.
thanks, Dave