Problem: Ducts creak or bang when furnace cycles on and off.

Cause: Expansion and contraction of ducts.

Solutions: Operate the fan continuously to reduce expansion and contraction.

Modify air ducts.

• Put resilient pads between ducts and supports as shown in Figures 26a and 26b.

Figure 26a - Modification To Furnace Air Ducts To Correct Expansion & Contraction Noise

Figure 26b - Modification To Furnace Air Ducts In Wall Cavity To Correct For Expansion & Contraction Noise

• Add braces with resilient pads where panels flex. Identify locations by listening and/or touching.
• Fasten acoustic duct liner to the inner face of ducts to reduce vibration of duct walls and noise transmission along the duct.

Continued.......