Do you ever feel a little sad or disappointed when an achievement "pops", but doesn't make the telltale "popping" sound? I think it's important because sometimes you might miss the fact that you got an achievement at all.
@technoupdatenow: I think it's just in certain games or parts of games when the unlock sound is eerily silent. As for the popping sound going when you're in a game and one of your friends logs on and you think you got an achievement...that's an entirely different issue! ;-)