setVolume problem

hi
I tried to control a background music volume using this code


soundInstance = new Sound();
soundInstance.attachSound("1");
soundInstance.start(0,999);
_root.soundInstance.setVolume(10);

here attachSound(“1”);
“1” is a linkage identifier. everything works perfect…music plays and volume decreases.
but not only the attached sound… the whole movie volume changes even the swf I’ve loaded in my clip. I just need to control the background music(“1” linkage) not all the sounds. what’s the problem here? how can I make this happen?

thank you