How to quiet a noisy forced-air system with This Old House

Watch this video from This Old House to learn how to quiet a forced air system.
Steps:

1. Mark center of start collars on the return and supply side of the heating duct.
2. Cut holes in sheetmetal ducts using a drill fitted with a circle-cutting jig.
3. Attach start collars to duct with ¾-inch self-tapping sheetmetal screws.
4. Install bypass damper between the two start collars; fasten damper with sheetmetal screws.
5. Seal seams around start collars with foil tape.
6. Adjust the counterbalance weight on bypass damper arm.
7 Turn on furnace to ensure bypass damper opens.