Hi guys, I have a little problem, I did buy a Macbook Air mid 2013 11 inch CTO 8GB of ram for like 2 months ago. I have only used Mavericks on it so I don't know if it's Mavericks or HW problem. I did update from ML to Mavericks. Some times like when I open a folder from the dock, I use "Grind" as view option. I can get a little white line at the screen, the line do pop-up at the place there the folder shows but it disappear right away. It's not on the hardware it looks like that the line is in the software / Video. I did test Apples HW Diagnostic and it do not show any kind of error codes so I guess that it's not a HW problem? Can it bee because of that I did update from ML to Mavericks and that I did not do a clean install? Or is it simply a bug in Mavericks? I know that I can install ML and try, but the recover partion is Mavericks and it 'll take time to re-install ML so I wanted to ask you first. So what do you think? Edit: I have tried PRAM reset now, option+cmd+p+r in startup. But still I'm wondering what you think, is it a HW error? And I don't know if it did fix the problem or not.