Take her outside on a leash when the pump is running, and just walk calmly by it as if it were not there. Distract her with praise and talking, have her do a "sit" and whatever other commands she knows, then praise her. Do this every day, make it part of her routine, and soon she will forget that scary monster that eats small dogs - I mean heat pump is even there!

Remember dogs' hearing is far more acute than ours, so it is likely even louder to her!