Our unit even thought the thermostat is set too on on the fan the blower slows down but not all the way when the unit turns off and speeds up too full speed when the unit comes on instead of staying at full speed that's why you thought you heard the blower turning on and off when the unit turned on and off even though the fan is set too on on the thermostat idk why it's like that but it doesn't bother me too much Edit: Tbh I feel more air movement when the air is on then when the heat is on idk why I do but I do it still blows all kinds of air in heat mode just I feel more when the air is on then when the heat is on Edit 2: I'm sorry I couldn't get a good shot of the flames in the furnace Edit 3: And ignore one of my cats towards the end of the video