Preventative maintenence inspection on Trane XR80 furnace. 20x25x1 air filter is new today. Clean flame sensor and check ignitor. Visual inspection of burners. Brenda mentioned a vibration noise when first turning on. Upon initial test run, bount that two screws on the exhaust motor were loose and allowing the motor to vibrate. Tightened screws and test ran system in heating mode. No more noise heard. Temperature rise is within specs. Blower and inducer motors tested good. 4" galvanized B-vent in good condition and no sign of leaks. 0PPM CO detected during testing. Furnace is operating properly, efficiently and ready for Winter.