In a regular visit in a home, I noticed that there was a irregular noise out of the furnace in the utlity room, so I took a look and made a video. See
After asked our maintenance staff check and fix the issue and here is what he shared. (see pics link below)
the diagnose by the maintenance staff is as this
the cooling fan on the inducer fan motor was broken
what is the cause, and how to prevent it from happening in the future?