We hear a high pitch whine like the noise you would hear from a ceiling fan coming from our air intake vent which is located on the wall in the bedroom when the furnace is on. Did not notice it when the AC was on. The vent does not seem to be loose. Is this something serious that I need to have checked out?

Is this the air intake for a high efficiency heater or are you referring to an air intake as the air return? Inside or outside the house?

Sorry, It is the air return. I do not know about a high efficiency heater. The vent is inside and located on the wall in the bedroom.

Take the grill off the wall and see if you still get the noise.

Could be a loose vane in the return or a duct fitting that is resonating. With AC, the air is moved faster and may not get to or is past the resonant frequency. Take off the return and see if you can see anything in the duct.

Thanks so much for you input. I will certainly take a look inside the vent.

I have the same happening and when I press on the wall the noise stops. Its either a loose vent duct or a ghost messing with me :)

Thanks, I appreciate your advice.