Digital BW, The Print

I have MIS K4 inks in an R2400, and this works very well for color.  I 
recently bought a ColorVision PrintFix Pro Suite, and I'll use Paul's 
method of making an icc file for printing through ABW mode soon.  Before 
going through this, though, I thought I'd make some quick prints just to 
get an idea of how they'd  look on Silver Rag.  The files are from scan 
of 35mm HIE.  As a result, there's a lot of grain (which I don't mind 
for these images.) When I print them, either through a color profile as 
RGB files, or through ABW, I get vertical banding.  Basically, there are 
dark strips running down the print.  They are about 1/8th inch wide and 
they are spaced about 1/8th inch apart.  I send 480 dpi files to the 
printer, and I tried a couple of different images.  Any ideas?