Ben Markson wrote:

On the audio WAV I have extracted here, there is a long section
of distorted "flapping" in the background during narration and
commenting. I haven't been able to get rid of it using more
modern programs without destroying the entire bass of the clip.
Basically, converting it to a mono radio or telephone frequency
is the only way. Does anyone know what this happens or what I
could do to remove this distortion?

May I suggest you start at the beginning ? No-one's heard your wav
file.

What happened ?

What do you mean by a " more modern program " etc....... ?

Graham