The most likely cause of the creak is the unclanging latch of the ducts (more than 10). To remove the violin, remove the cover from the duct and verify all the latches.
If all the latches (including those that fasten the air duct to each other), they need to lubricate the silicon grease (preferably odourless). If the blinds creak, they need to be treated with thick grease.
