No, I don't think that should bother you. I can't hear it. Now, the device must be able to dissipate the heat easily... Otherwise the fans might go off. And as they are small you could hear them

I have a UDM SE in my living room under the TV (for lack of alternatives). My UDM SE has an additional SSD installed because I also use it for video surveillance of my house.

When there is silence, you can hear it clearly. However, it does not interfere when you are watching TV, etc.

If you are reading a book at three o'clock at night, with the windows closed and in complete silence, you will hear the fan. Otherwise, it's probably louder when you walk through the flat...

No offence, but why don't you run it in a rack as it should be? Don't you have any other devices? Switches, Synology, etc.? A bit overkill then a UDM SE. Then maybe this would be something for you: https://store.ui.com/collection...

I also have it running in the living room under the TV in the sideboard.
Without HDD / SSD it is noiseless, even with sfp 10gbit, because no fan starts.

I don't think so, unless it's really absolutely quiet at your place, in which case you might hear a fan...