Noise in a residential air vent can be caused by debris in the duct work, such as nails and plastic, that rattles when the air flows through. A loose register vent can cause a sharp rattling noise when the screws need to be tightened.
When the HVAC system is experiencing a lack of return air flow, homeowners may notice a high-pitched sound. This sound indicates that the air filter is clogged, the duct dampers are closed on the unit or the air supply is blocked by an object.
When the air conditioner or furnace kicks on and the air flow begins, a blowing noise may be audible.