I have the same problem.  I get a line that runs length-wise on any page that is scanned/copied using the auto document feeder.  Any help is appreciated.

I called Dell support, who told me that it was in fact the scanner mechanism malfunctioning, and that it would cost more to fix than the machine was worth so I should just be happy to use it as a printer and make copies and input faxes one page at a time.  Oh, and it didn't matter that it had been less than six months since they sent me this replacement printer, I was still out of warranty and out of luck.  Thus, sequential failure of a product and any replacements they send you takes you beyond the warranty.  My response was not charitable.  Needless to say, I do not intend to purchase a Dell product again, ever.