Mac sound problems

I have an Apple iBook, about three years old. For the last few months, the computer has been freezing or slowing down significantly and the sound becomes choppy and continues to be choppy even after the computer resumes operating normally. The sound doesn't lag at all, I just get indistinguishable bits of what I should be hearing. Sometimes it takes a reboot to fix, and other times I only have the shut the program down to fix it. This happens from any source, not just streaming videos. It will happen during non-internet activities as well. I'm suspicious of an over-heating problem, but recently when I've had this problem I put the computer on freezer packs and it doesn't seem to chance the performance. I have Apple Care and I'm wondering if the source of the problem may be something that I can fix under warranty. It is happening more and more frequently, to the point where it occurs about every two hours of use. At the very least it is really annoying and any potential solutions are greatly appreciated.