Arrived for callback. Client described a noise coming from the outdoor system. Upon arrival set thermostat to cool and went outside where I heard a vibration coming from the fan motor. Disconnected the unit and checked all electrical components. Everything looked normal. Turned unit back on when the noise was not present anymore. Made sure everything outside was on tight. Checked system pressures. Everything was normal. Switched unit to heat, everything sounded good. System is operational.