Digital BW, The Print

Hi everyone,
I'm so impressed by the massive amount of knowledge that seems to be 
present in this group that I'm worried I might be about to lower the 
tone!

Anyhow, I use a Canon ip5000 to print black and white images 
predominantly only hammered texture greeting cards, however the 
output on the high quality setting is oddly green/yellow tinted.  
This only happens on high quality, oddly it's perfect on standard and 
grayscale settings.  I've tried changing the colour balance and it 
doesn't help.  If I could I would simply print on standard but can't 
because the image has those annoying 'printhead' lines through it 
(despite having just replaced the printhead after 6 months use!!) and 
I can't print on greyscale because the back of the cards features 
colour and invariable the front will have colour lettering.

It makes no difference whether I change the paper to plain or photo 
paper and seems to have no effect when I print from a different o/s 
or port?!  Plus it doesn't change if I use Canon or 3rd party inks?!  
Ooh and I've tried converting all images to CMYK on the offchance 
that that would help and although it produces a slightly better 
effect the tint is still there!

Does anyone have any ideas as to what I might be able to do?!  I'm 
losing the will to live on this one!!

I'm so sorry if this kind of issue has been previously covered, I had 
a rummage through messages but didn't manage to find anything!

Wishes & stardust,
Ophelia