Preventative maintenence inspection on Tempstar furnace running in great condition. 20x25x4 air filter in good condition. Clean flame sensor and check ignitor. Visual inspection of burners. Flush condensation trap and drain lines. Run test unit in heating mode from thermostat. Temperature rise is within specs. Blower and inducer motors tested good with no unusual noises. 2" pvc flue in good condition and no sign of leaks. 0PPM CO detected during testing. System is operating properly, efficiently and ready for Winter. Bob expressed concern about an unusual noise from two vents, one return in the master bedroom, and one supply vent in a bathroom. During test run, no unusual noises were heard from either vent, or from furnace. Suspect thatcit is the vent grills vibrating. Recommend trying to re-mount return vent to ensure it is not loose, and inspecting supply vent to ensure there are no parts that are loose. If return vent grill vibrates when tight to the wall, it may be necessary to r