What's causing my duct work to pop when the furnace starts or stops? A popping noise is a typically sign of an under-sized duct design. It may be attributed to greater air flow than the duct work is built for. Have a qualified company analyze your home's ventilation system for proper design and recommend adjustments. Improper duct work layout can be attributed to a variety of ventilation and air quality problems, including: loud popping higher energy bills lowered life of the system uneven airflow throughout your home damaged compressor in summer overheated unit in the cooler months In addition, if your ductwork is undersized you may have other issues, such as leaky ducts and poor layout that impacts airflow. In humid climates this can encourage mold growth within your ductwork.