Non-automated volume increase

I'm using Logic Pro 9.1.8. Lately I've noticed that during playback certain tracks, both audio & midi, will bizarrely increase in volume. The fader will leap from, say -5db to +1db. I have tried automating a consistent volume throughout but in some cases the fader will jump up in volume regardless, with automated volume on or off. Obviously, this is a major problem. Anyone have any ideas as to why this is happening or ideas about a possible solution?? Thanks ..