The fan on the AC180 is running all the time and is too loud to have in a room or tent/camper.
Bluetti support have not been able to give me an answer. I am guessing it must be normal operation.
I would not purchase it again for inside use.
The fan runs based on incoming or outgoing load as well as high temperatures. It should not be running all the time as you state. Is it indeed running all the time or are certain incoming or outgoing loads occurring or warm temps exp. immediately after charging.