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Old 02-11-2020, 02:04 PM   #1
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Carrier gas furnace rattling sound when heat stops


I have a Carrier MCB58 gas furnace and since about two weeks it started making a rattling sound when the heat stops (transition from heating to fan circulation only). The filter is new. The blower is clean. The sound seems to be coming from the inducer.

Here's a video of the noise (noise starts at 0:24 secs). It sounds like a dirt bike engine.

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Old 02-11-2020, 04:11 PM   #2
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Re: Carrier gas furnace rattling sound when heat stops


Once that fan spins down, probably just a frequency that resonates where a couple of pieces of metal are touching.
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Old 02-11-2020, 04:51 PM   #3
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Re: Carrier gas furnace rattling sound when heat stops


There are no pieces of metal to touch as the inducer on a high eff unit is all plastic.

If the furnace is less than 5 yrs old it may have a 5 yr parts warranty. If the inducer is off balance or failing then maybe a Carrier dealer can get it under warranty. You have to pay for the labor to install it.
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Old 02-11-2020, 05:02 PM   #4
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Re: Carrier gas furnace rattling sound when heat stops


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Originally Posted by yuri View Post
There are no pieces of metal to touch as the inducer on a high eff unit is all plastic.

If the furnace is less than 5 yrs old it may have a 5 yr parts warranty. If the inducer is off balance or failing then maybe a Carrier dealer can get it under warranty. You have to pay for the labor to install it.
Thanks Yuri. The furnace was installed in 2008 so I'm out of luck for the warranty. The inducer is about 390$. Not cheap
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Old 02-11-2020, 05:16 PM   #5
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Re: Carrier gas furnace rattling sound when heat stops


That furnace is on the list of those affected by the class action lawsuit.
It’s a 58MCB right?
When was the last time it was serviced and checked out?

http://hipspro.com/pubs/Furnace-clas...led_notice.pdf
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Old 02-11-2020, 05:34 PM   #6
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Re: Carrier gas furnace rattling sound when heat stops


Yeah you should get it checked by a Carrier dealer to see if the heat exchanger is failing.

Those inducers spin at close to 2000 rpm and over 3000 rpm on a mid efficiency so they can get off balance and vibrate.

That is one of the larger wheel diameter types and can be noisy due to inertia and it's mass. Also the motor mounts may be worn and not soft and absorbing vibes like when new.

However it may run like that for several years if you don't mind the sound.
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Old 02-11-2020, 05:39 PM   #7
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Re: Carrier gas furnace rattling sound when heat stops


Quote:
Originally Posted by roughneck View Post
That furnace is on the list of those affected by the class action lawsuit.
Itís a 58MCB right?
When was the last time it was serviced and checked out?

http://hipspro.com/pubs/Furnace-clas...led_notice.pdf
Correct. That's the model number. But I was under the impression that mine (post 2007 model) had the new heat exchanger in. It came with a 25-year warranty on the heat exchanger. I double check just to make sure. Thanks for the link
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Old 02-11-2020, 05:40 PM   #8
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Re: Carrier gas furnace rattling sound when heat stops


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Yeah you should get it checked by a Carrier dealer to see if the heat exchanger is failing.

Those inducers spin at close to 2000 rpm and over 3000 rpm on a mid efficiency so they can get off balance and vibrate.

That is one of the larger wheel diameter types and can be noisy due to inertia and it's mass. Also the motor mounts may be worn and not soft and absorbing vibes like when new.

However it may run like that for several years if you don't mind the sound.
Thanks again for your input. I will call the Carrier dealer tomorrow to schedule a service and to take look at the inducer. The sound is quite annoying but I could live with it (maybe not my wife).
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Old 02-11-2020, 06:31 PM   #9
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Re: Carrier gas furnace rattling sound when heat stops


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Old 02-11-2020, 07:07 PM   #10
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Re: Carrier gas furnace rattling sound when heat stops


Sounds like the bearings on the inducer are starting to go.
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Old 02-11-2020, 09:09 PM   #11
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Re: Carrier gas furnace rattling sound when heat stops


Quote:
Originally Posted by yuri View Post
There are no pieces of metal to touch as the inducer on a high eff unit is all plastic.

If the furnace is less than 5 yrs old it may have a 5 yr parts warranty. If the inducer is off balance or failing then maybe a Carrier dealer can get it under warranty. You have to pay for the labor to install it.
I was figuring more on the sheet metal body of the handler itself, but you guys are definitely the authorities on these things as compared to me.

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Originally Posted by user_12345a View Post
Sounds like the bearings on the inducer are starting to go.
I am deferring to whatever these two guys and the other seasoned HVAC pros on here are saying.
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Old 02-11-2020, 09:40 PM   #12
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Re: Carrier gas furnace rattling sound when heat stops


I'm no authority nor a pro - the others know much more than i do.

You're not wrong though - if the inducer vibrates a lot, it can actually cause the entire return drop to make noise, I've heard it - it's more metallic and goes away mostly when the blower comes on.

The noise in the video does sound different from that - but you never know.
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Old 02-12-2020, 06:09 AM   #13
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Re: Carrier gas furnace rattling sound when heat stops


It could be end play in the motor or the motor growling as it slows down or dry bearings in the motor. Have to be there to see it and feel for vibration.

I replaced a lot of those inducer fans on the ECM motor MVP models under warranty from vibration. Plus that ECM motor and some ECM motors have a unique sound.
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