This happens fairly often and is pretty annoying. (Although I think your IDE is great! But there will always be one or two things. )
I usually have several souce files open at once. The tabs run along the top border of the editor window. Every so often a tool tip kind of thing displays along the top, covering up the tabs - and it has a tendancy to stay there.
The tip always seems to contain the contents of a line several lines above the top line in the window. For example, right now the top line I can see in my editor window is line #10. The tool tip shows the contents of line #4. Usually lines are long, which means the tool tip usually covers up several tags, which means you can't see which files are which.
And it's a pain to get the tool tip to disappear; if you could just click and have it be gone that wouldn't be so bad, but it usually takes me a few or several clicks to get rid of it.
I have tried looking through all of the (too many?) settings so I can disable this, but I didn't find anything - probably because I don't even know what this particular thing is.
I hope I've given you enough info so you can tell me how to disable whatever this is.