audio recording – What is this waveform doing?

The thickness of the line (the distance between peaks and troughs in your waveform) remains about the same, so there is no “disturbance” however, rather than your waveform remaining about a zero centreline, something has changed over a greater timeframe than audio frequencies – which is why you cannot hear it.

As to what it is, could be a reference voltage not held strictly when something else in your environment started to draw current, or maybe even something as simple as someone opening a door to the recording room.