I built one and used it for a while before giving it to a friend for his bday as he fell in love with it and then built another which I haven't boxed yet. No hum coming from either though. Can't remember if the layout already includes some sort of power filtering, though I'm pretty sure it had a cap between 9v and ground. The low value resistor Mark mention could be a useful addition but, should it not be already included, I wouldn't put the hum down to the lack of series resistor on the 9v since in my experience it's not a "humm-y" build?!