I have a heat pump. When the air conditioner comes on it sounds normal then after a few seconds I hear like a swooshing noise coming from the air handler in the attic. It makes the noise then stops then few seconds later does it again.and keeps doing that every time.We had to have freon put in the unit a month ago. Then the other day we had the guy come out again because the outside fan would not cut off. He said we have a bad defrost knob so he unhooked the wire for the heat and hooked the air conditioner wire to it. He said before winter we need to get a new control board. Does any of this have anything to do with the noise from the air handler?

It sounds like the unit may still be low on freon, the noise your hearing is in the liquid line.