Thank you for your question. There could be several causes and factors, which could be a source of noise, within a fan unit. If the unit has been installed for quite some time, I would suspect a dust build-up on the blower wheel which has caused an imbalance or the duct work may have become constricted. If this is a new installation, it could a vibration or the blower wheel could possibly be rubbing on something. For further assistance, please call our Technical Support group at 800-637-1453.
Date published: 2014-08-19