You said it, not me.
By the way- I hear those same sounds after waking up each morning!! But those are much better than the noises I make when my five year old had a bad dream and is standing point blank at the edge of my bed at 2AM!!!!
No really, I have heard that noise for over a year and not really thought anything about it. I would guess it plays some important role or else they woudn't have it do that. I wonder why it is louder on the Macbook- maybe your metal casing on the powerbook makes it quieter than on plastic? My iBook is somewhat noisy but never bothers me much.
solution---> turn up you radio a little more and you won't hear it.