There are many reasons your ducts may pop or make banging sounds. Usually, noises occur after your air conditioner or heater turns on. As air begins cycling through the vents, ductwork expands. This metal expansion leads to occasional popping or banging. Other causes for duct sounds include:
Air balance problems
Differences in supply/return pressure
Temperature changes that cause metal to contract or expand
Air leaks, dirty filters & undersized ducts that whistle
Depending on the reason your vents are noisy, Cool Experts’ technicians might recommend fiberglass duct wrap or acoustic duct liners to quiet metal duct work. Placing rubber pads between vents and wood beams or other building materials may dampen annoying sounds. Duct cleaning, sealing and insulation may help balance the airflow and minimize noise.