-I got some advice
-I got a piece of advice.

-there was lightning
-there was a flash of lightning.

-I heard some news.
-I heard one piece of news.

could you tell me the difference -if it exists - in the pairs of sentences? these sentence are from my book. all nouns above are uncountable nouns.

I guess each pair of sentences has a similar meaning, but if there is a subtle difference, let me know please.

I think each noun in the first sentences is used as an uncountable noun in itself, however the noun in the second sentences is used a little like a countable noun by the structure "OF" although they are still uncountable nouns.

am I thinking right?
Your reasoning is correct.

I got some advice-- it could be a lot
-I got a piece of advice. -- one bit only

-there was lightning -- maybe all night
-there was a flash of lightning. -- just one instantanous manifestation

-I heard some news. -- could be several items
-I heard one piece of news. -- One juicy item only (this is not a common utterance)

In all of these, I would say that the form with 'some' is the usual expression unless there is particular context for a single case.
thanks. you helped me.