Are they actually equals signs or a constant line?
Could it be that you have the Tools, Autocorrect, AutoFormat As You Type option for either headings, Borders or Tables turned on?
When I turn those on and put a number (3) of equals symbols next to eachother I get a solid double line across the page - is that it?
You can obviously switch off that option or, to get rid, select text either side of it and go to Format, Borders and Shading and choose "None".
Hope this helps.