[RMcNeal]

Assuming yours is similar setup to my 2019 3791RD, the "furnace" option in the bedroom does nothing, but will kick on the fan in the AC unit. That may be what you hear. Our rear unit has the heat pump, so I can run it when cold down to about 40 degrees. The furnace is gas only and controlled by the thermostat in the kitchen, and uses the ducts in the floor. The roof top unit does not come on when in Furnace mode, only the gas furnace.
Incidentally, I can actually use the heat pump when colder out as long as I supplement it with electric heaters and/or the fireplace. Saves on propane.