My house was totally remodeled and I upgraded with forced air and a heat pump. I have a supply vent in every room, yet only 2 return vents... one at each end of single story house.
Only the return vent closes to the furnace makes an annoying whining sound (wa, wa, wa, wa... is only thing I can say it really sounds like). Does anyone have any suggestions to make this sound go away?
When I shut down the entire system, the noise goes away. If only the fan is on, the sound comes back. Could there be a bearing of something going out on the fan? Or possibly something else?
Please help before I lose my flipping mind!

Yes, it could be a faulty motor, or out of balance wheel, but when a return grill is near the furnace, you will almost always hear the blower noise through the return. Was the noise always there since install, or is it a new occurrence? If it was always loud, Id say there isn't much you can do, other than insolate the inside of the return duct(may not help much). If it's a new occurrence, then I would definatley have the installers back to check blower assembly. Good luck and please let us know what you find.

Thank you... I'll get on it and let you know what's the solution!

Brand and model number please? I know of a few fixes for this sound for a few brands.

I'm really not sure if this is the info you're looking for but:

York Diamond 80
G2FD Series

If not then please let me know what other info you need. Thank you very much for any advice!

Sorry, not sure. Design of ductwork is on possibility. Check filter, if that has an ECM motor it can wind way up to a very high speed if there is restrictions in the airflow.

So... called the AC guy and he stopped by. He listened to the sound and said he knew exactly what it was... pulled out some pliers and twisted the damn vent baffles... said it's kind of like if you blow on a blade of grass and make whistle noise from it. Haven't heard the noise since he bent them! Can't believe how easy of a fix that was and I never thought of that! Thanks for all your hints!

Thanks for the update. Glad the noise is gone.. Good old harmonics.