The answer to 'air duct odor' is that there are several common causes, including mold, dust, pet dander, and even decomposing animals. Symptoms may include a musty or foul smell coming from the vents, as well as visible debris or buildup in the ducts. The best solution often depends on the root cause, but generally involves professional duct cleaning to remove the source of the odor.
For minor odors, you may be able to DIY by vacuuming out the visible dust and debris in the ducts. However, for more significant issues like mold or animal remains, it's best to call in a professional HVAC cleaning service to thoroughly inspect and clean the system. They have the right equipment and expertise to identify and eliminate the odor source safely and effectively.