Hi
I have the same problem with my Unibody 13" from late December 2008, Bought at a local Mac supplier in Denmark. But at first I did not do anything about it, because I had read this thread, and seen people claim that Apple would not fix it.
But then a couple of weeks ago, my screen started making this strange noise when closing the lid, definitely from the Hinge. Then I decided to take contact, with the store where I purchased the Macbook, I told them about my problems, and without hesitating they sent the book, to a certified Mac workshop or whatever it is called, now yesterday I was told that they will change the Display and Logic board!! And as I can see, changing the logic board, must be to fix the audio problem.
So maybe there is a chance for my book to work as it was meant to be. Anyways, when I receive the book back, I will let you know whether the problem is fixed or not.