Furnace clean and tune. Cycled system. Checked heat exchanger, ok. Checked, removed, and cleaned burners and flame sensor. Both ok. Checked igniter, ok. Checked and tightened electrical connections and clamps. Drain line clear. Checked and adjusted gas pressures to maximize efficiency efficiency. Found gas valve was whistling, adjusted pressure down on high fire to lessen noise. Preformed combustion test, normal levels found . System operating normal at this time. Job complete.