If you have not already resolved this issue, we suggest you search our online knowledgebase for this product: http://www.support.xerox.com/support/phaser-7760/support/enus.html and please search on Streaks. The Case titled "Light Lines or Streaks or White Vertical Lines (All Colors)" will give you some things to try.
Alternatively, you can visit our Contact Us page for other support options.
My office's Phaser 7760 has an odd printing issue: an entire streak of of the page is printing, like it has been "wiped" without being printed. On a letter size piece of paper it appears on the bottom, on tabloid it is along the left side of the page (pictured).