Performed preventative maintenance on furnace. Customer changed filters. Inspected blower assembly, heat exchanger, heating components, burners, flame sensor and overall condition of furnace. Customer had concerns about a noise she was hearing from the furnace, and wanted to know what it might be. Upon startup the inducer motor was vibrating a little, and would become a little more noticeable under a load. I adjusted the idm wheel a few years ago to keep it from vibrating as much. The bearings are wearing down and causing vibration. I made homeowner aware of what was causing the noise. I cleaned the flame sensor and brushed dust off the burners. Checked and tested thermostat operation, wiring, capacitors, amps, pressure switch, safety switches, temperature rise and gas pressure. Customer wants to see how long system will last before needing repairs or replacement.