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 is able to manage. Have a qualified company analyze your home's ventilation system for proper design and make necessary recommendations. Improper duct work layout can cause several ventilation and air quality problems, including: 

1. loud banging noises
2. higher energy usage
3. lowered lifespan of the system
4. uneven temperatures throughout your home
5. damaged compressor in summer
6. overheated unit in the heating season

In addition, if your ductwork is incorrectly sized you may have other issues, such as leaky ducts and poor layout that reduces airflow. In humid states this can encourage mold growth within your ductwork.