I am looking at buying a cloud core router but I am wondering how loud the fan is inside. I need to have something that has decent performance in a quiet environment.

See this video https://www.youtube.com/watch?v=UNwxAjJ4V4A
It is full load

Does the fan increase speed with load or is the speed always the same?

It increases with load. Just plugging in an ethernet cable or removing it, you can hear the fan change speed.

Ill be ordering a CCR for home use next week, I do think it will need to be modified with at least a better fan(s) (quite) for me to use it where I intend to place it. Could be its OK when idle but when loaded I get the impression that it screams and would like to be in a server room instead.