Furnace Whistling/Squealing

[TimJ2021]

I have a Payne furnace. I hear a whistling or high-pitched squealing sound whenever the inducer motor kicks in.

Thinking it might be a bad bearing, I replaced the inducer motor but the sound has not changed. I push on various parts of the furnace and motor (carefully) when it is running to see if it is a vibration. I can detect only very slight changes in the sound when I do this. The fan blades are not contacting the motor mount. Maybe it is instead air rushing through an opening, but the noise is quite loud - can be heard a couple of houses away.

Any ideas as to what to check next?

Thanks,
Tim

 

[Reach4]

Is there a belt, or is the squirrel cage on the motor shaft? Guess you would have mentioned a belt if you have one.

 

[Sponsor]

 

[TimJ2021]

Right, there is no belt. It is direct drive with the fan attached to the shaft using a set screw on the flat.

 

[Fitter30]

Take a pic of front of furnace door off and name tag theres just to many furnace configurations.

 

[TimJ2021]

Three images attached

 

[TimJ2021]

And with tag....

 

[Fitter30]

Did you replace the blower wheel and inspect it normally being in the path of flue gas can't get it off without egging it. When remounting ventor assembly did you use any high temp sealant to seal the housing to the heat exchanger?

 

[TimJ2021]

I did not replace the blower wheel since it comes on prior to the inducer motor spinning up. When it is just the blower spinning, I do not hear the noise and so left it alone.
When I remounted the inducer assembly, I used a new gasket (felt or some type of paper). This is the only thing I changed.

 

[WorthFlorida]

Is there an AC coil anywhere? If your thermostat has a "FAN" and "AUTO" position, move it to fan. This will only run the blower only and not the inducer.

If the whistle noise is only when the inducer motor runs and the neighbors can hear it, look outside at the exhaust vent. It maybe plugged up causing the noise. Doubtful that your neighbors hear it if it was inside the furnace.

 

[TimJ2021]

I've run the furnace with the faceplate off and the safety interlock defeated. I can see the inducer motor startup as the noise begins. It also sounds as if the sound is coming from the bottom half of the unit.

Do these things ever hit some kind of resonance frequency when the air rushes through just right?

 

[WorthFlorida]

You just need a small opening anywhere to cause a whistle noise. At my air handler for AC, my son can hear a whistle at the filter grill and I cannot. Flexing the grill around and filter the whistle goes away.

Since you feel it’s the airflow from the inducer fan, check around the burners. This would be a good time to clean the air intakes to the burners, even expose the plenum looking for corrosion.

 

[Fitter30]

Furnace looks like it was made week 18 of 1996. Pull burners get a telescopic mirror good flashlite and inspect heat exchanger looking for crack or a baffle that has rusted away. Combustion analyzer is needed to really check it. 25 year old furnace is past its life span.

 

[TimJ2021]

Furnace looks like it was made week 18 of 1996. Pull burners get a telescopic mirror good flashlite and inspect heat exchanger looking for crack or a baffle that has rusted away. Combustion analyzer is needed to really check it. 25 year old furnace is past its life span.

 

[TimJ2021]

I know it's been more than 3 years since I posted this. I've lived with the noise since then. Couldn't take it anymore yesterday, so I opened up the furnace to take another crack at it. And I found the issue. I am posting it here in case anybody else finds it useful.

I identified the solution by spraying water around the inducer motor housing while it was running. When I did this, there was an audible pitch change in one spot. The water temporarily blocked an air leak so that the noise changed. Realizing this was the source of my whistle I applied high-temp RTV sealant to this small gap and, voila, no more noise.