I have a forced hot air furnace, installed in September 2002, located in the basement. The blower motor is belt driven, single speed. While the blower is running it you can hear it all over the house. The return air grill is located out side of a bedroom and during the night when the blower comes on it is so loud that it often wakes us up. What can I do? Can I use a muffler? The ducts is 12X12 rectangular. I suspect that the noise I hear is vibration and air flow through the duct. Is any noise reduction material available that I can use?

What is the duct made of? My guess is that it is galvanized sheet metal fastened rigidly to the furnace. The blower vibrates, and shakes the furnace and the attached ductwork even if the motor and blower have rubber mountings to reduce the noise. What you could do is cut the ductwork loose near where it connects to the furnace, but before the filters. You want a gap, doesn't need to be very wide, the kerf an abrasive saw blade might be big enough. Support the duct so the 2 ends line up. Wrap duct tape all the way around carefully pressing it in place to seal well. The furnace will still vibrate, but not the ducts.

If you are getting noise out the supply vents too, you could do the same thing there.