Hello,
I had a problem with my right speaker, too! It would cut in and out. I did find, however, that if I adjusted the balance all the way to the right and played music with a lot of bass, it would probably get the speaker working properly. Eventually, I took the book in and got it fixed. It was a quick repair.
Of course, when I got my iBook back, it started turning itself on and off. So, I had to take it back in and they replaced the logic board. I wonder if it was a coincidence?
James