XNA "SoundEffect" Issues...

Basically, this sound won't stop playing when I release the mouse left click button. But it should. No errors, it just doesn't work. Ideas?

SoundEffectInstance c4soundsf = C4Sound.CreateInstance();
                if (mouseState.LeftButton == ButtonState.Pressed && previousMouseState.LeftButton != ButtonState.Pressed)
                {
                    c4soundsf.Play();
                }
                if (mouseState.LeftButton != ButtonState.Pressed && previousMouseState.LeftButton == ButtonState.Pressed)
                {
                    c4soundsf.Stop(true);
                    c4soundsf.Dispose();
                }