Canon Pixma MP780 Fax Problem (horizontal line)

This unit puts a broken horizontal line across the bottom of the page on all outgoing black & white faxes sent from the ADF only. It seems to be an image of the edge of the page? Relevant info: -Over 8 weeks, my original unit was completely rebuilt in Canon repair shop and then made the same line. Canon has sent 2 more refurbished units since then and still the same line. The last tech I spoke with said he tested one in their plant and it does it there too. He even said the Pixma MP830 (upgrade of this model) puts out that same line. -4 units did this over different locations -I have changed my phone/fax cord 3 times and faxed from different locations -Outgoing faxes sent from the plate glass and directly from my computer are fine (no line) -Faxes sent in color are fine, even from ADF -All incoming faxes are fine (no line) -Black & White COPIES from the same ADF are perfect (no line) -All other copying, scanning, printing is fine (no line). -Horizontal line is only on outgoing black & white faxes and only when sent from ADF. Is this an unfixable manufacturing flaw/defect or does anyone else have any ideas? After 2 months, Canon tech support has pretty much given up on this and doesn't know what to do. I will try to force a refund if this can't be fixed since I need it for outgoing faxes mainly and it is not very professional looking. It seems strange to not be fixable since lesser priced fax machines from many manufacturers don't do this sort of thing consistently on every page in the same spot like this. Any suggestions would be GREATLY appreciated.