screeching noise everytime gas furnace shuts off

Our house was build in end of 1995 and we have two gas furnaces in the attic -- one for each floor. We are the second occupants of the house. The original furnaces are still in place and I have not had any maintenance done on them over the last five years. I do regularly change the filters every 4 months.
Over the last week or so, one of the furnaces has been making a screeching metallic noise when it is about to turn off. The noise is now loud enough where it can be heard downstairs. The unit does seem to be functioning...
Any pointers to what the problem could be?
Thanks.
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I dunno.... what do you do with you car when it starts making a "screeching metallic noise"?? Do you put it on the internet?? or do you get a mechanic to see whats wrong with it and have him fix it??
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Time for maintenance. Based on my experience (as a homeowner, not a tech) anytime a mechanical item makes a noise like you describe, it would be best to shut down that furnace before something more serious goes wrong.
Since the main moving part in a furnace is the blower fan, the sound you hear is likely the bearings in the motor or the fan wearing on each other. You hear it better when the fan stops spinning as it will gradually slow down hitting the right frequency to attenuate the sound. when spinning the noise is probably at a high enough frequency you can't hear it with your ears.
If it is a bearing, and you continue to operate the furnace, the bearing can eventually fail such that it welds itself together, preventing the motor shaft from turning any longer. This will cause the motor to overheat, and hopefully throw a circuit breaker on the motor, or blow a fuse on the controller.
Best case, the motor may need to be replaced. Worst case, the stress of driving that failing bearing over time has caused the controller to be damaged. Considering the age of the furnace, that could mean difficulty finding reasonably priced replacement parts leading to just out and out replacing the furnace.
Only a HVAC tech is going to be able to tell you exactly what is going on, so I suggest you call one before the thing finally fails when you really need it, and you have to pay weekend or emergency rates for the tech.
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Mike H wrote:

Thanks for your response. I live in the Roswell (suburb of Atlanta) and just setup an appointment with Central Heating & Air (got that name from homereports.com) for tomorrow. I am hoping that their techs will be competent :-)
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chuck wrote:

Chuck;
The furance is in the attic? If so, it's lying on it's side. Likely the blower has come loose on the shaft and needs to be pushed back into postion, and the lock nut tightened. Good luck though, usually [since H.O. refuse to shut it off] the lock nut is just loose enough for the blower to move down and nick or wear a groove in the shaft making it a bitch to move back. You might be looking at a new motor [since the shaft is ruined,] and a new blower wheel, [since the hub is now elongated and worn.]
--
Zyp



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my guess would be "draft inducer", only reason i say that is because you have stated you have made an appointment with qualified people in your area,
let us know what you find out

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My money is on the gerbils screeching with joy now that their run is over...
wrote:

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The Freon Cowboy wrote:

Thank you all for your responses. It was the blower motor. It was replaced this morning and the noise has gone away. Along with the noise, $340.15 has also gone away.
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wrote:

$340 is about right for the motor replacement, plus service call, and sales tax, the total should have been somewhere around $450 - $500.
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That's a decent price it it sounds like they were more than fair on the motor price as that is where it can get pretty expensive depending on the HVAC unit and what is required vs. what will fit.
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chuck wrote:

Not a bad deal. Consider you didn't have to dispose of the hazardous "e" waste, and you got a warranty. Not really bad at all considering you didn't have to pull the furnace and take it the shop. [Like your car maybe.]
--
Zyp



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wrote:

didn't
Dont they have oil ports anymore ?
--



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wrote:

nope
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