Sound porblem in FCE4.0.1

I have a six sequence project 'nested' in the Timeline of that FCE4.0.1 project. When the sequences are opened, one at a time, the music tracks play just fine. When seq 4 is opened, rather than stay nested, the music track often, but not always, suddenly drops in volume. Then a bit further on it regains the lost volume. So - each sequence opened - all OK, when nested, one music track, often, has a sudden drop. Can anyone solve this for me? Perhaps relay the whole piece of the music.

James Bowman