Hums, rattles and hisses... Oh my! The tranny isn't gone until the car stops moving.
Turn up the stereo and forget about it. Of course changing the fluid can not hurt and maybe some anti-slip goop to thicken it up. Does the hum get louder when the transmission is hot or is it the same when it is cold? There is a carrier bear on the rear drive shaft but that is always turing even in neutral. How noisy, loud is this hum?