Arrived and discussed issue with customer. Customer stated aim floor systems outdoor unit was make a metal on metal sound. I tested system indoor and outdoor units. I checked refrigerant charge and amp draws on outdoor unit. At this time I could not duplicate the noise the customer reported. Everything sound currently is normal operation. I did notice possible low refrigerant charge and also dirty outdoor coils. I recommend getting a maintenance plan and discussed option with customer. If noise comes back we will warranty our diagnostic fee and only charge for repairs.