Digital BW, The Print

I am using a Nikon 5000 with the Nikon software for Tri-X and Plus-X 
negatives.  I find better results scanning for "color negative" and 
scan at 16 bits, 8X (seems to reduce scanner noise), and neutral 
settings on all the other controls.  At 100% on screen (1:1) I see 
small areas of posterization, especially in shadows, but also sometimes 
in midtones.  These areas do not seem visible in the prints or at lower 
resolution on screen.  This makes no sense to me.  Any thoughts?  Does 
Tri-X, with that long, shallow toe, actually look like this?  Scanner 
settings?  Could the monitor itself (Sony LCD, 5K, 2.2) be doing this?  
Thanks.