said by elitefx:
Have the heat exchanger etc inspected when you get the blower shaft replaced.
I had the most bizarre experience with a HVAC guy today. I heard him hit the furnace with a tool when I was not looking and then he claimed that the heat exchanger was leaky and that the furnace must be condemned.
After I insisted there was absolutely no evidence of a leak until now from my CO monitor, he sort of backed away but still applied a wide metal tape on the supposed leak location. He was then trying to sell us a new furnace at a supposedly huge discount. I showed him the door.
*** Sincere thanks to everyone for the suggestions.
a) I put filters on each floor vent and the cold air intakes and the blower sound is muffled quite a bit. I can live with it until I gather up the courage to change the blower speed from HIGH to MED.
b) The clang was actually coming from the damper after the humidifier. I duct taped it open for now although that surface gets quite hot when furnace is on.
c) My son admitted to rolling some marbles down his floor vent in the hope that "they will fall into the flames and melt". They did not come out near the blower and I can't locate them because of bends on the ducts going to his 2nd floor room. However, they are not causing the grinding sound for sure.