Do you have an air conditioning or heating unit that seem to have restricted airflow? Did you know with reduced airflow the HVAC unit will lose its efficiency? What this mean is you'll be paying more for your utilities.
In order to avoid this, filters should be replaced and the air ducts should be regularly maintained. The reason why is with clean air ducts and filters, there is no obstruction that would get in the way of the airflow. It will be a stable flow from beginning to end.
Also, consider the type of filter that is being used in the duct system. There are a few types: fiberglass, polyester and pleated filters, high efficiency particulate arrestance (HEPA), and washable air filters. The filters to use are dependent on the person and the environment they are in. Call your local contractor to find out.