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