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 able to manage. 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 usage lowered life of the system uneven heating & cooling throughout your home damaged compressor in summer overheated unit in the heating season In addition, if your ductwork is the wrong size you may have other issues, such as leaky ducts and poor layout that reduces airflow. In humid states this can cause mold growth within your ductwork.