Furnace clean and tune. Cycled system. Checked heat exchanger. Found rust and corrosion in all chambers. Deep etching found in one chamber. This is where heat exchanger will crack at some point. Checked, removed, and cleaned burners. Ok. Checked and cleaned igniter. Ok. Tightened and checked electrical connections and clamps. Found some weak clamps on the condensate lines. Found ventor motor bearings are worn. This is causing excess heat and noise. Preformed combustion test and found normal levels in exhaust. No CO found in airstream. Average life expectancy for this unit is 14 years. This unit is past that threshold and is in worn condition. Due to age, condition, and cost of repair, second opinion is recommended. Future failure is expected. Job complete.