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 provide a written recommendation. Improper duct work layout can cause a number of ventilation and air quality problems, including: loud banging noises higher energy bills lowered lifespan of the system uneven temperatures throughout your home damaged compressor in hotter months 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 impacts airflow. In humid states this can encourage mold growth within your ductwork.