What's causing my duct work to pop when the furnace starts or stops? A popping sound 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 make necessary recommendations. Improper duct work layout can cause a number of ventilation and air quality problems, including: excessive noise higher energy consumption lowered lifespan of the system uneven heating & cooling throughout your home damaged compressor in cooling season overheated unit in the cooler months In addition, if your ductwork is the wrong size you may have other problems, such as leaky ducts and poor layout that impacts airflow. In humid climates this can cause mold growth within your ductwork.