When Microsoft Word opens the RTF file, it wants to show you when/where the data is inside a table. So you will see faint gray gridlines in Word. These lines should not show up in Print Preview mode or when you print the document.
Depending on the version of Word that you have, there is generally a "show/hide" gridlines -- either an icon on the ribbon or a menu choice. SAS can't control what Word displays, so you'd either have to look at the document in Print Preview mode or you'd have to toggle the show/hide gridlines options inside Word (I think it might be under the TABLE menu???)