Furnace runs but makes loud banging or booming noises at startup or shutdown.

Safety warning: Booming at ignition can indicate dangerous delayed ignition. Turn off gas and power and have the furnace inspected if the noise is severe.

• Check registers: Open all supply registers to reduce duct pressure and expansion noise.
• Inspect burners: With gas off, remove burners and clean rust and debris from ports. Ensure burners are properly seated and aligned.
• Support ductwork: Add hangers or braces to large sheet metal ducts that flex or pop loudly.

Gas pressure and combustion adjustments must be performed by a qualified technician with proper instruments.