Unfortunately because the warranty is 60 days out of date, I very much doubt that Apple would replace your device under warranty, though it's true that it doesn't hurt to ask.
I think downwithvista might have misread your question as a display problem. I do not believe that your sound issue has anything to do with the screen (LCD) or HDD. I'm assuming you've tried switching out headphones, and it's not just a pair of headphones you're using. That would seem to narrow it down to the logic board.
Because I'm relatively new at these repairs though, I'd get a second opinion before replacing it. If someone does confirm that the logic board is the likely culprit, this is the part, and this is the guide you can use to replace the logic board.
Hope this helps! :)
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Are you saying the sound through the headphones is different? Same headphones and EQ settings?
crwdns2934271:0crwdnd2934271:0 David Hodson crwdne2934271:0