The past several months my forced air furnace would all of a sudden start making this high pitched chirping sound and then get even louder throughout the night. When we would shut it off it would squeal until it shut off completely making us think it was a belt. We had used wd-40 and it seems to help a little but not completely. We have had repair men come out several times and every time they do the squealing stops and they can't detect where it is coming from. Also, the filter's clog up less then a month and we have already had to replace two ignitors in the past 3 months. What could be causing all this?

You should never use a lubricant on a belt. That belt is designed to grip, not to slide.

It could be the belt, but also could be the sheet metal of the furnace itself... or the squirrel cage if you have one.

The only real way to narrow it down is to get to it when you hear it. Put your ear all round it to see if you can narrow it down.

Cleaning the ducts might help the filters plugging. Also think about what could be causing extra dust. When you change the filters, can you recognized anything on them?

Belt driven blowers are notorious trouble makers. Most newer furnaces have gone to direct drive. Examine the belt if you have one. If it is smooth and shiny, it is glazed and needs replaced. Make sure the new one if fairly tight. Some rely on the weight of the motor to keep the belt tight. Make sure it is free to pull the belt tight.

If it is not a belt drive, post back and I will have some other ideas.

Some are quick to say call a professional. On the other hand, I see many questions like yours where it didn't work. It may take a while, but you should be able to find the problem.

On my fourth call to a heating and cooling place they first told me to spray a lubricant on it. But thanks for letting me know not to do that. The technicicans have also said, it could be off balance at times but they have never done anything because it always stops before they get here.

I have tried to listen but it's hard since after the furnace was installed they repaired the wall and if anything has to be changed... the wall will have to be taken out to do so. And there isn't much room to see anything. I did check out the belt but that doesn't seem to be where the noise is coming from.

The filter's are just filled with massive dust, not much else.

Are the motor and blower mounted solidly or are they free to shift, and rub on something? You might even be see scraped places where things were rubbing. If so tighten or replace the screws that hold it.

Have a goodman furnace that chatters. On the inducer motor there is a squirrel cage with a small fan. The fan keeps warping and hits the cage. Have had the motor replaced 2 times but it still keeps doing the same thing. The last time it got so bad it completely locked up the motor. Still trying to find someone that can remedy this problem. Hope this helps