The answer to 'air duct greasy' is that greasy air ducts are a common problem in many homes, usually caused by a buildup of dust, dirt, and grease over time. Symptoms include visible grease on the ductwork, decreased airflow, and a musty or dirty odor coming from the vents.
In many cases, homeowners can clean the air ducts themselves using a duct cleaning kit or by hiring a professional duct cleaning service. However, if the ducts are severely clogged or there is mold or other contaminants present, it's best to call in a professional HVAC technician who can properly inspect and clean the system to ensure it's working safely and efficiently.