| What do the black marks look like? flecks of black, patches of printed black, solid black, light black?
What is the backgrounding colour, does it vary, if varying does it vary from top to bottom or left to right?
for backgrounding usually cleaning all the electrical contacts in the EPU and TF unit should solve the problem.
Black flecks on the page after one print could be due to the paper being to thick or the fuser not hot enough which peels off toner on the first copy and then gets it stuck on the next copies.
but need more info to work out the problem | 
Linear Mode
