I have an air duct in my basement. It leads from my furnace (I think?) to the outside world.
However, as you can see from this video, it is "twitching".
Every second or so it jerks slightly and makes a noise.
The portion of the duct shown in this video is the end of the duct that terminates outside the house. The rightmost portion of this duct leads to an opening on the exterior wall of the house.
When the furnace switches on, the twitching stops. What's going on?
Do I have an alien living in my air-duct?
Update: The end of the duct is not connected to the furnace. It is connected to a clothes dryer. But I still don't know why it is clicking like this.
Best Answer
The outside end of the duct has a flapper to prevent air (and critters) from coming into the house when the dryer is off. However, even with the dryer off, there can still be a small amount of airflow through the duct, e.g. from inside/outside air pressure differences. It seems that in your case there isn't enough airflow to keep the flapper open, so it swings closed, making a "click". Then, as the (small amount of) pressure builds up, the flapper pops open to let a burst of air through. The changing air pressure causes the flexible duct to throb. Repeat twice a second, and bingo: alien living in your vent duct.