This is usually normal. Terrestream schedules a SEN66 fan self-clean around 10 AM local time on Tuesdays.
It should be brief. The cleaning cycle lasts roughly 13 seconds and may show a cleaning animation on the light ring.
There is a cooldown. The firmware avoids repeating the cleaning cycle too often; manual cleaning is also available from device controls.
Contact support if it is constant. A short weekly sound is expected. A fan sound that repeats often, never stops, or appears with other device problems is worth reporting.
