I bought my iMAC a little over three years ago and am now getting many vertical lines on my screen. They are transparent and only can be noticed with certain color backgrounds. They occur over the entire screen and seem to be getting more prominent. I am not covered by apple care and the closest store is 2 hours away. Not wanting to pay the fee for the phone call, I will probably take it in when I am in another city visiting. Just wondering if anyone else has these lines, what was the cause? I have attached a photo to explain. Please help!