For some time now my Mavic's fan does not turn on and so the drone overheats very quickly when it is not being flown. It used to be quite loud, and now it doesn't even make any sound. Is this an issue or a setting?

There is no setting for the fan. I recommend you discuss the issue with support.

Hi Lucas.GM1, how long is the aircraft on?

DJI Mindy Posted at 2017-5-4 01:10
Hi Lucas.GM1, how long is the aircraft on?

Sometimes for 15 or more minutes, but it gets blazing hot and eventually shuts down from overheating.

Lucas.GM1 Posted at 2017-5-4 12:04
Sometimes for 15 or more minutes, but it gets blazing hot and eventually shuts down from overheating.

Did you crash the aircraft before?
It's probably a hardware issue.  I would suggest you to send it in for further evaluation.