Digital BW, The Print

I print B&W with an Epson R1800 with three cartridges of Eboni and QuadTone RIP. I just reloaded it after long hiatus. After getting a clean nozzle check, I made a print (landscape orientation).  It looks great except for one thing.  On the left side of the print (which comes out of the printer last), there is a vertical band, about 3/8 inch wide, that is slightly darker than the adjoining area. It may actually be two bands, the outer one darker than the inner.

I remember having occasionally seen this before, and I'm wondering if I'm exceeding some minimum margin limit.  The print is letter size, 8.5x11 inches.  My right and left margin for this print were about .28 inch.  I don't have this problem with a color version of the same file on my R200 printer using the Epson driver.

Anybody know what causes these bands?  Must I set my margins wider than some specific width to avoid it?  Or is there some setting in QuadTone RIP that I need to tweak?

--Peter