Sound doesnt work in Loaded movie clip

Hello,
I have a movie clip that has a sound in it, used using the Sound class (attachSound) - it works just fine when I run it.
BUT when I try to load it into another movie clip, say I have a parent clip and i load this one into it, the sound doesnt work.
If i include the sound as part of the parents library, then it DOES work, but the parent file size is now much bigger.
Any ideas?
mR