Don't do it! A PSU like this needs airflow. It's noisy because the only way a small fan like this can generate some airflow is if it spins really fast. If you replace it with a Noctua which can generate enough airflow, it also will be just as noisy. If you replace it with a Noctua which can't generate enough airflow it's gonna be really dangerous. A PSU that overheads can easily kill your hardware, it can even catch fire.