I got a 2008 Ford Taurus with 128k miles and automatic transmission. Whenever I first turn on the heat or air conditioning, the front passenger's side vent makes a bumping sound for a couple seconds and then goes away. I've learned to live with it over the years and have not had any problems with airflow or air circulation. I think there might be a door or flap of some kind inside the vent that keeps getting stuck when I first turn the system on. Any ideas?
yes those doors can warp from heat over time, causing it to bind.
Its possible its a flap/door that keeps getting a bit stuck. I don't imagine it is a huge problem, since there is a good airflow. Maybe change you cabin filter? Check for leaves or debris.
It could also be the fan going out and makes that sound until it gets going.
