Thing is, your PSU has no idea what programs you are running, all it sees is your computer wanting more or less power and that's all it ever needs to know.
That PSU has a semi passive mode which means no fan is on when the computer is only using a small amount of power. It will turn on the fan when the computer wants more power and turn it off again when not needed.
I believe the way the psu is designed means that every time the fan is turned on or off, it will click.
If you close discord, get a graphically heavy game running and then open discord I suspect you won't hear anything because the fan should already be turned on.
If that is what happens then I would say it's simply discord pulling just enough power during start up to briefly trigger the psu out of passive move and into turning the fan on, then off again because it stops using the cpu so much after its fully started.