Not sure what you mean with "tiny sound fluctuations"? An effectively useless description.
You missed however to tell the used digipot type and how it's connected in the circuit.
Just in case, notice that the analog potentiometer is exposed to an AC voltage, to avoid distortions, a digipot in this place would need a dual power supply. Or be connected slightly different, with DC bias and capacitor at the pot ground node.
Or does "fluctuations" refer to crosstalk of the digital control signal? This can easily happen.