EDIT: The original fan had a bearing problem, so this isn't a valid comparison. Yes the noctua fan is quiet, however the old fan was broken.
Quick comparison video showing how much quieter the 40mm Noctua fan is versus the noisy stock fan. It's essentially silent now. The fan you're hearing is from the power supply in the background. This is on a Monoprice Maker Select V2 printer.
![](https://i.ytimg.com/vi/6lnb1HBw3GI/maxresdefault.jpg)