Following Dave's advice, I closed the door
For my setup (set and forget, not THC), there are two very small fans a top rail at the back of the humidor. They really do look a lot like CPU fans. The loudest noise in my unit comes from these and they are far noisier than the fans on the large humidification units.
I also plan to ask Bob Staebell about the fan specs so that I can just buy some low noise replacements. The whole experiment would only cost about $20 total, so worthwhile from my perspective.
In 36 hours, the unit is already so stable that the humidification units aren't coming on very much at all. But the noisy fans are every 20 minutes by design.