High indoor humidity can trigger a poor air quality reading. The sensor interprets moisture as particulate matter, causing an automatic fan speed increase.
Override the auto mode. Press the fan speed adjustment button (labeled 'auto/mode') to cycle out of auto mode. Manually set it to Low, Medium, or Sleep speed. The unit will run continually at your selected speed.
If that didn't work, ensure the air quality sensor near the control panel is not obstructed by dust. Wipe it gently with a soft, dry cloth. The sensor requires a 10-20 second calibration period after powering on.