Ac clean and tune. Customer stated that they heard banging from the system last night. After turning the fan off for a few mins, the noise went away. Cleared drain line. Cycled system. Checked and cleaned electrical compartment. Tested compressor, tested lower, but within normal range. Tested fan motor, tested ok. Used coil cleaner on condenser coil. Hooked up gauges and checked pressures and temps. Subcooling was 10 degrees, indoor coil was at 43, indoor temp split was 20. System has some signs of getting worn, but operating normal at this time. Average life expectancy for this unit is 14 years. Checked fan blades and mounts. All were secured. If noises return, customer to call us back. I could not find any reason for this noise at this time.