A ducted heat pump's outdoor unit carries the full heating and cooling load for the entire house, which means it runs harder and more often than a wall unit serving a single room. Increased noise usually points to one of a few causes.Debris such as leaves or built-up dirt around the outdoor coil can restrict airflow and make the fan work harder, increasing noise. A loose cabinet panel can vibrate or rattle during operation. In coastal areas, salt-related corrosion on internal components can also affect how smoothly the unit runs over time.A sudden change in noise, rather than a gradual increase, is worth having checked promptly, since it often indicates a specific component issue rather than general wear.