Loud fan sound when turning on A/C

That would be the main cooling fan switching on as the A/C commands it on to increase airflow over the condenser. It will run at full speed then slow down as the A/C senses the drop in the refrigerant temperature. This is normal behavior but you might notice it more if the condenser or radiator cooling fins have any dirt blocking some of them which reduces the airflow and causes the fan to run longer as the air doesn't move as well. I would suggest using an air nozzle to blow out any dirt from the radiator and condenser. Just be sure to blow it out the front of the cores.