Where did this bizarre background noise come from?

Hi Kay,

I took a look and a listen.

The original recording level was quite low, about -18db

Is this the usual level you record at? A higher recording level will help the signal to noise level

ie how loud the voice is compared to background noise.

In the image above I've normalised the audio to -1db and then selected the noise in the gaps

between words.

You can see in both the spectral frequency display and the frequency analysis window the nature of the noise.

It's sitting here ( after normalisation ) at roughly -55db

It's uniform across the spectrum 10hz - 20khz and beyond.  This is classic white noise.

As to causes, it's not likely that you have "hit a button".

More likely it will help to record at a higher volume.

It's possible that an audio lead in your setup could cause this if it's starting to go faulty or perhaps you

have moved your recording setup to a more noisy location either audible or electrical.

If you don't have a way to re record this, it should be possible to remove it.