Noise or not, I see it but don't hear it

In the last and now the NEW version, When I record from something streamed via SPDIF, When there is no sound ‘0’ volume the waveform shown is thickened. going into smaller and smaller time segments, There seems to be something there. I found that I can Grab the center (horizontal) bar and drag it up or down ever so slightly, and this oddity goes away, but when I save it it comes back. Now I can’t hear anything but I wonder if that is some sort of low-level NOISE?

I have some VERY heavy Noise canceling on my Ethernet Intranet and the main line to the modern is air-gapped.

Using Win 11
EVGA NU audio card
SPDIF optical to stereo

I don’t know…

You can run the Amplify effect to see (and hear) if there’s anything there. (Just select & amplify the suspect part and the default amplification will give you a clue about the noise level.)

On the regular linear scale, the waveform usually disappears around -30 or -40dB, where you still can hear it. The exception could be subsonic or ultrasonic noise. DC offset (zero Hz) is also inaudible except at the beginning & end when it suddenly kicks-in a and kicks-out.

Noise is an analog problem. Digital audio corruption (or dropouts) is usually very bad and obvious, if you get any audio at all, but sometimes it can sound like a click or pop. As an analogy, one flipped-bit (a one instead of a zero or vice-versa) in your bank account is just as likely to cause a 1-cent error or a billion dollar error.

Sometimes ground loop noise (such as AC hum) can get-into the analog electronics through a digital ground but usually digital isn’t an issue.

I do wish I could upload a short file for you to look at and listen to. Even which I use can’t upload here.