This is a pretty old question, but I thought I'd add my 2 cents. I've tried the above solutions, including the ghost css, which I will definitely be saving for future use. But none of these worked in my situation. Here's how I fixed my issue. Hopefully this will help someone else.
Open inspector (or whatever your preference) and starting with the first div in body tag, add display: none;
to just that element. If the scroll bar disappears, you know that element contains the element that's causing the issue. Then, remove the first css rule and go down one level into the containing element. Add the css to that div, and if the scroll bar goes away, you know that element is either causing, or containing the offending element. If adding the CSS does nothing, you know it was not that div that caused the issue, and either another div in the container is causing it, or the container itself is causing it.
This may be too time consuming for some. Lucky for me, my issue was in the header, but I can imagine this taking a bit of time if your issue was say, in the footer or something.