Paragraph Return lines showing in print on indesign

[H A0D4C]

Please help - I have a manuscript in indesign cs6 (old i know!) - when I click on the preview (screenmode > presentation) or export to pdf, horizontal lines in black appear where I have paragraph returns and page breaks. 

How can i remove these? 

[H A0D4C]

I have checked if there are any paragraph rules on, these are both not ticked. I can't figure out what else it might be. 

[Colin Flashman]

Within the paragraph style, could it be a paragraph border? rule above or below would have been my other choice, but i'd rule out strikethrough or underline given that it would appear in all of the type, not just the last line.

[Peter Spier]

Can you share a sample of this file?