Natural Gas Furnace Clicking Noise

Hey all, Furnace Rookie here. I just moved into a 30 year old house with a 17 year old thermopride 80% efficiency 80k btu furnace.
Got my first heating bill back for December, 300 bucks, OUCH! is that typical? I'm in SE Michigan.
Here is my question though. When the furnace cycles on, it starts up normally, and runs fine, hot air at the vents ect. however, when the gas shuts of mid cycle and the blower fan continues to run, the furnace makes a clicking noise kind of like the sound that old baseball cards made when put in the spokes of your bike. this clicking slows down, and then stops, all the while the blower fan continues to run without making a sound.
I opened the main panel of the furnace, and it looks like there is a second smaller electric fan in there? The furnace vents thru a 4 or maybe 5 inch steel pipe up the chimney. Its sounds to me like there is a second fan (or something else that is spinning) that runs when the gas is burning, and stops when the gas shuts off.
Thanks for your help
Dave
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get your make and model and search google for the manual.
in the meantime, the one blower may be to move the air to the house. the other little one may be to blow the flue gas up your chimney.
in buffalo ny put your gas billing on balanced billing, unless you make more money in winter.
general furnace article not repair at: http://www.bobvila.com/ArticleLibrary/Task/Building/ForcedAir.html
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get your make and model and search google for the manual.
in the meantime, the one blower may be to move the air to the house. the other little one may be to blow the flue gas up your chimney.
in buffalo ny put your gas billing on balanced billing, unless you make more money in winter.
general furnace article not repair at: http://www.bobvila.com/ArticleLibrary/Task/Building/ForcedAir.html
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here's the manufacturer http://www.thermopride.com/technical.cfm
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You probably have an inducer blower which is a sort of exhaust fan for flue gas (aka the smoke) on higher efficiency furnaces. This will typically shut off with the gas burner when the thermostat says enough already, or may remain on a bit longer with a time delay to clear the gases out of the heat exchanger and reduce corrosion.
You're saying you only hear the clicking when the gas burner shuts off? Does it continue until the main blower shuts off or just briefly as the inducer coasts to a halt? Could be dirt on it. Many inducer motors have a small fan to cool the motor and this will be a fan you can probably see when you take off the outer furnace door. The inducer blower itself is a squirrel cage blower wheel in an enclosure drawing on the heat exchanger and blowing out the flue pipe. Without periodic attention the cooling fan and motor (and perhaps a finger guard over the fan depending on type) may get very dusty dirty.
Observe while it does its thing and shuts down and see when and where the clicking is occurring. If you do see a visible motor cooling fan you can...with furnace power off or at least turned off at the thermostat...try giving it a spin. It should spin freely on its bearings (the blower wheel you can't see, the motor rotor, and the fan you can see should combine to a little bit of mass that if free from obstructions and on good bearings given a push will spin easily for good bit). On the other hand just observing normal operation seeing how long it coasts when it switches off.
It's also possible that the clicking could be nothing more than furnace components contracting after the burner shuts off and making various clicks and pops on account of that and being old.
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yes, once the burner stops, the noise starts, gradually slows down, then stops. the main blower is still running when this happens.

I'll take a look at it when the motor is running, it just started, ( I think) so, it could very well be a dirt thing

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Zephyr,
I had a similar issue with my heat pump. One day out of the blue it started making that "baseball cards in spokes" sound when it shut off. It progressively got worse, and I found that hardly any air was coming out of my vents, causing the heat pump to run almost continuously. I had it checked, and it turns out that the bearings in the blower motor were going out causing the blower to scrape against it's housing. I know we're comparing apples(electric) and oranges(gas), but blowers are blowers. It could be that the bearings are going out on that secondary blower.
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Is it possible that the clicking sound is there the whole time, and you just don't hear it? Listen to the heater very carefully.

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