When I turned on the furnace my client said, "It sounds like the house is vibrating."
The crushed vibration damper.
A vibration damper does just that. It is intended to dampen, or eliminate, any furnace vibration transferring through the house via the metal duct work.
And in this house there was a noticeable vibration.
Things settle over time.
Supports that hold up a heavy metal duct tube, like the one to the right, can sag, or come loose.
When that happens gravity takes over!
The vibration damper is a rubber membrane that separates two sections of duct work.
In the case to the right it would be on the return side of the furnace. There would be another one over the furnace itself.
The purpose is to separate the furnace, and its vibration, from being able to transfer through the house when the unit turns on.
In this case the damper has crushed such that one section is now touching the other.
When the furnace turns on a noticeable vibration is the result.
My recommendation: I tell my clients to learn as much as they can about their systems and listen to things when they are operating as intended. That way, if something goes wrong, an unusual sound may be an indicator that there is a newly-developed issue. In this case a loud vibration was something my client was not used to, and viola!, she could identify it. Checking around I found the source of the noise. Sounds, and listening to sounds, is definitely a part of home maintenance.
Jay Markanich Real Estate Inspections, LLC 
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560
