I have a similar issue... It's not so much the "sound" of people having fun, but for me, recreating with my imagination people having the fun they had, and me not being there.
For instance, many of my problems come from a girl who I care infinitely about, but was too shy to say "yes" to her when we were in high school. I look back and it's simply too late. I have no issue with other people having fun in life, including her, but when I think, and I imagine her at the parties that I skipped out on years ago... It just hurts. It's like, "Why couldn't I share that with you?"
It's a weird thing. It hurts in the stomach area for me, quite literally I'll have take an antacid pill just to keep from getting an upset stomach when I think of it. So much of our pain stems from psychological issues that in turn make us feel pain physically.