I've been experiencing some banging noise in my vents when the furnace shuts down. It would sound like somebody knocking at the front door and it travels down the length of the vent. I just had the pilot burner and inducer motor replaced. The house is warm, but I'm still getting the clanking noise each time when it shuts off and every so often when it starts up. Any ideas and/or suggestions as to what it might be and how to fix it?

Was the noise there before repair? Tech possibly dropped a plastic cap, wire nut or other small object into the duct and the air moves it along and when it shuts off, drops back.

The noise was there before the repair.

I have seen some older metal ducted returns get "oilcanned" and will pop in when turned on and then back out when it turns off. I would suggest along the ductwork and try to pinpoint the spot. It could be heat expansion but you usually don't hear it along the pipe, it's more like a drip. Let us know what you find. Brian