The fan noise on my n5200 was really unsatisfactory. I tried several other 92mm fans but all were either too noise or didn't cool enough. After much experimentation I cut a bigger hole in the back plate and mounted a 120mm Noctura (although Yate Loon might be better and cheaper) and replaced the five 1T enterprise drives with three 2T Seagate green drives. So far so good; the drives only get to 42C during heavy use.
Even so, the n5200 is still the loudest box in my office so it only runs a couple hours a day while other hosts do scheduled backups.