Furnace Hum

[gear]

I hear an annoying hum in the bedrooms of my home whenever the furnace runs in low speed. The hum appears to go away when in mid or high speed. The furnace is a variable speed Keeprite. The bedrooms are the only rooms with return vents and the only rooms that experience the problem. I've tried removing the vent covers, thinking that air restriction could be the issue; no avail. Any ideas???

[Atticmonkey777]

Time to call a pro.

[gear]

Did some further investigation; 3 of 6 return vents in the house had been completely boarded over presumably during a previous reno. When I opened up the closed vents, the noise went away (air restriction afterall!). I still don't understand why there was a hum on low speed and not on high. Is it possible that there is a lower frequency vibration at low speed and less audible frequency at high? Strange to me...

Thanks Atticmonkey, there is no questioning the value of an experienced Pro. In this case a little applied common sense solved the problem!