Can anyone explain this?

Narration audio divided up into sections to match relevant video clips.
5 second audio clip drops out for 2 secs in middle.
Audio completely disappears, levels drop, etc., then reappear.

Here's the bizarre part:
Double clicking on the audio clip in the timeline and playing it in the viewer = plays no problem.
Dragging the same audio clip to another place in the timeline = plays no problem.
Positioning a different audio clip in the same place=plays no problem.
Re-importing the audio into the timeline from the master/source clip = no problem, until I place it back in the required place.

There is 1 track of video and 4 camera recorded audio tracks above it.
The narration track is track 5, 7 & 8 are music.
At the offending point in the timeline, there are no video effects or dissolves, no audio dissolves and no music.

I have cleaned up the audio by dropping the level to -inf on a couple of frames; but I've tried removing the audio keyframe marker points and reinserting them, but it makes no difference.
Dropping the clip to track 6 or any other track at the same marker point still results in audio loss.

Unfortunately, I do not have another take of this particular line of narration dialog.

Any thoughts,
Thanks,
T.

PS. David, I hope you are feeling better!