Thin horizontal grey lines that look like method separators but aren't.

As the title says, these look like method separators, but they are disabled in the settings and I have turned off their colours. 

They are very thin and appear between lines. They appear whenever I scroll through lines using the arrow keys and go away when i do something else. This has been happening ever since i got PyCharm which was I believe a few months ago.

Any help would be appreciated, and thanks in advance!