The answer to 'air duct odor' is that it is commonly caused by a buildup of dust, debris, and microbial growth in your home's air ducts. Symptoms include a musty or unpleasant smell coming from your vents, and in some cases, respiratory issues or allergies. The solution is to have your air ducts professionally cleaned, which involves using specialized equipment to remove the accumulated contaminants.
While you can attempt to clean the ducts yourself using a vacuum with a long hose attachment, it's generally recommended to hire a professional air duct cleaning service. They have the necessary tools, expertise, and safety protocols to thoroughly clean your ductwork and ensure it's free of odors and potential health hazards.