Digital BW, The Print

Anyone seen this before?

I am using EZN in a C86 and am getting VERTICAL banding i.e. parallel
to the paper movement through the printer. It only occurs in once
place, and that is about 2 inches from the edge of the page on the
side where the head parks. The affected area is about half an inch
wide, and appears to be symmetrical. The bands are small variations in
density (but clearly visible, enough to ruin pictures) and run the
whole height of the paper (when printed in portrait). It does not in
any way look like the banding you get from missing nozzles (my
vertical bands are fuzzy), and I am pretty convinced that the nozzles
are OK. 

I have tested this by printing out the purge patterns for each of CMYK
so as to eliminate any errors from scanning (which I first thought the
problem was) and the bands are there in all colours.

I took an A6 test page I printed with one of these and put it back
into the printer. The centre point of the bands seemed to line up with
one of the high spots in the black undertray where there is foam to
catch ink, and I am thinking along the lines of there may be a high
spot here where the ink is hitting the page at strange angles. I am
also thinking what I can do to investigate further, and I would be
grateful if anyone has any experience.

Thanks in advance

Steve Taylor