Dell 968 AIO copies have strange boxes

When I make copies on the printer from the document feeder, the copy has grey boxes that weren't on the original document.  The example below was generated by making a copy of a blank sheet of paper.  The number, size and darkness of the boxes varies from copy to copy.

Printing a document from my computer works fine.  Scanning a document to my computer gives a normal scan.  If I have no original document and hit the copy button, I get a blank sheet of paper.  If I scan a document from the flat bed, I don't see the unexpected boxes.