Digital BW, The Print

Ok, ...I guess they say that when something sounds too good to be 
true...

Have made a bunch of b&w prints with my new hp 7660.  All the smooth 
tone digital images print out near perfectly, but from film scans 
the "woven" dither pattern somehow blends with the random scatter of 
the grain and produces a hidious pattern of perceptible soft 
gridlines which almost look like microbanding.  Looking at the prints 
under a loupe shows that it is some interaction between the grain 
pattern and the dither pattern however.  The problem manifests itself 
most in something like a face in a portrait or other smoothly shaded 
objects and vanishes in more texture rich images or grain free 
images.  By comparison, the posterization issues with my 1160 seem 
rather mild now.  I've tried upsampling to printer resolution prior 
to printings which changes the output, but doesn't correct it.  
Anyone else seeing this?  Anyone have a solution?  Unless I figure 
out a work around I will be returning the printer as the output from 
T400CN scans are not suitible for hanging in a gallery.

thanks for any advice,

mark