20w50 oil is real thick when cold, add in lifters bleeding down and it doesn't surprise me that it takes a while for the noise to go away.

What oil filter are you running? It is a known issue with certain filters that have bad anti-drainback valves for this very issue to occur.

I would do an oil change to a lighter weight oil, 10w30 VR1 would be fine, and a good filter, Wix 51515 is my preferred choice.

Being in Italy though, I do not know what your choices are.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.