Followed in your tracks as above, got this:OK, it's no mystery what Mosquito Killer does. The blue waves on the timeline don't change but the whine goes away.
The first step in Mastering Suite (Low Rolloff—Rumble Filter) shouldn't be visible, either.
Effect > RMS Normalize to -20dB.
Effect > Limiter: Soft, 0, 0, -3.5, 10, No.
Noise Reduction of the Beast (6, 6, 6) using the first 1.5 seconds of the clip as Profile or reference.
Not identical twins with your results, but at least fraternal, and the patched recording sounds good to my (admittedly untrained) ears.
Is my takeaway here that, assuming the creeks don't rise and no other mishaps occur, and nothing else goes awry, my new booth placement, microphone setting, and additional padding will produce future recordings to which I can apply similar corrections and get similar results?
And to verify, the Audacity Audio Book Guide says
so consistency is required with that effect.Once LF-Rolloff is used, you have to use it on all chapters. It changes the voice just enough so the sound is not transparent. It is required the chapters match.