The AC to DC converter has a fan that normally runs when charging the battery; it should not run continuously unless your battery voltage never reaches a "fully charged" state. The fact that it stops when you "disconnect" the battery with the STORE switch points to that being the problem.
Some have a DC to AC Inverter as well with a fan that runs whenever the inverter is on. It may be wired to shut down if the batteries are disconnected with the STORE switch but most are not.
Ted & Melinda
2016 ACE 27.1
2016 Chevy Sonic Toad