Soundtrack Pro problem - audio changes speed

[Herbert Harris]

I put together a series of tracks (5 music and one vocal) and exported them as a single AIFF file. When I listen to the exported AIFF file in QuickTime, everything sound great............except one thing:

The voice track speeds up and goes out of sync with the rest of the musical transitions.

Is there something I am doing wrong? I've tried everything I know to prevent this from happening, but it still keeps happening.

Thanks,

Herbie