Random Black boxes on client start

There are random blank boxes appearing every time I start the client, similar to the popups you get if there is a notification. However, as you can see, the boxes are blank. There was one but now a second box has begun to appear. While nothing appears to be wrong, I am concerned that this may indicate there is a problem that the client is trying to tell em about and it is failing to render. Does anyone know what is going on here?