I was curious if anyone could help me with some diagetic/non-diagetic elements I am having some confusion with.  I get the basic idea but I thought of a couple of particular examples that I’m not sure I understand.

I understand that non-diagetic sounds come from outside the storyworld.  Recently I’ve watched some episodes of Luck on HBO, which is done by Michael Mann.  In his work he often completely silences the storyworld and inserts music instead.  This is pretty common in his work.  I know the music is non-diagetic, but what about the complete absence of the storyworld sounds?  Is that non-diagetic also?  And what kind of message might someone try to portray with this technique?

My other example comes from specific scenes in LOST or Walking Dead.  When a character whispers something to another character, and the audience is completely left out of the loop as to what was said.  Is this non-diagetic?  It doesn’t seem so.

Any clarification on these would be appreciated.