After thoroughly inspecting the furnace I could not find the slight tingling rattling sound coming from inside the heat exchanger. I checked all screws and all exterior pieces of the furnace for vibration and could not find the source. I remove the induced draft motor and listened inside the furnace and I can hear a slight pinging almost like a screw is bouncing around down in there. The furnace is 18 years old and the amount of labor and the cost of finding the noise is not recommended due to age and condition of system. I gave 4 options on replacement. Thanks Brian.