Hi, I just bought my Macbook Air a week ago. This is my first apple laptop. I'm quite satisfied with its overall performance. But occasionally, when I open a new window, a white (or slightly colorful) thin line appears on the screen. It gets disappear when I switch to another window. Here is an example https://docs.google.com/file/d/0B3292dIz9C_5cFVGT1pMbktrMkU/edit?usp=sharing So I'm just wondering, is there some problem with my machine? Does anyone encountered the same problem before?? PS. Mine is 2013 version i5 256G with 8GB memory.