I would still visit an Apple Store and see what they can do to fix it at the genius bar. Sometimes Apple will fix issues like this for free. Make sure your system looks well cared for (clean and in a good case) when you go. I suspect you have a hardware issue here.
* As the saying goes a clean & sharp looking person will get better service (it holds true for equipment too).
Make sure you have a sad face and ask for an estimate before they fix anything (if they need to take it in).
Let us know what happens - Good Luck!