First thing I'd try:
select the track
right-click and 'select whole' track (to highlight the whole track)
Track - Consolidate audio region
This helps clean up the start/end points of the audio

Also,
When using gain change make sure you have a valid track area selected. If the From-Thru settings are not valid it may err.


I do not work here, but the benefits are still awesome
Make your sound your own!