High pitch noise (feedback)

[juelze]

Hi there,

I originally posted this in another thread but it kind of got buried. We recently had a Goodman GM95 2 stage furnace installed and it's working quite nicely with one exception. Once the furnace comes on we'll get some nice warm air coming through the vents and then slowly but surely we get this loud high pitched noise coming from god knows where. It sounds kind of like a television that is on a channel when the station is turned off and there are all those colored bars. The noise comes and goes until the furnace is off. When the noise starts up (usually 20 seconds after the furnace kicks in) it gets progressively louder. Someone mentioned that the returns might be too big and cause a humming but this really isn't a hum but a high pitched noise. I went around and put my foot against all the vents in the house and it doesn't seem like they are vibrating. The furnace itself is pretty quiet. And to make matters worse half our basement has drop-tile ceiling that you really can't remove to get at some of the duct work. I'm thinking that too much air is blowing compared to our old furnace and this is causing a vibration and then the noise.

We are having the HVAC installers come back to take a look at it but I'm afraid this isn't something common and hence will have to live with it. Is this semi-common in the HVAC world?

-Ryan

[Chill]

It does sound from your discripton there is a air pressure problem. They should be able to check the install setup and make sure you have the proper air flow. You could even have a damper closed somewhere that is restricting air flow. Make sure all vents are open and none blocked.

It may be common to there installs, but its not common to my installs.

[docholiday]

Walk around your home and put your hand directly on all the return grilles. (open hand spread over the grille). Odds are one of them has a vibrating louver. It's just a frequency issue and a possible loose louver. If you find it you can either get a new grille or remove it and run a bead of silicone caulk down the center.

I think most of us here have chased this noise at least once in our careers.

High pitched noises are hard to figure out where they come from, I dont know why but our sense of noise direction doesnt seem to work well with high pitched sounds.

Imagine how your dog feels.

[juelze]

Thanks for the advice guys. We had the installer come out and he turned down the fan and said we should remove some louvers from some of our cold air returns. We removed them to allow more air to be sucked down and the noise went away.

Now, another question. Any reason turning down the fan on a furnace would be bad? Is it good to have it run at a higher speed in regards to have the furnace last longer?

Thanks again for all your wonderful advice!

-Ryan

[servtech2]

Yeah high pitch always throws you off, But do check the return, also sometimes screws are alittle lose and the grill vibrates... good luck with it

[Chill]

Most furnaces run on lower fan speed. They are always set up from the factory on low speed. So I wonder why the installers set it up higher. I am wondering what the temp rise was before and after they lowered the speed.