Samsung SCX-4521F / Fuzzy thin lines when printing from PC.

I have a Samsung SCX-4521F laser multifunction. About a dozen fuzzy thin horrizontal lines appear when printing via the USB or the Parallel Port. Some lines are tighter and darker but some are almost 1/8 inch in height and a little lighter. On some of the lighter lines you can make out fuzzy words, some of the same words that are contained else where on the document. The lines are spaced almost 1 inch apart and go horizontally across the width of the document. The printing problem still happens when I try to hook up any alternate computers to this printer / mutifunction. When using as a copier (stand alone - no computer) the prints are perfectly clear with no problems. I don't use the fax function.