I know the sound you are talking about. Something definitely kicks in after opening the door. Seems to be coming from the engine compartment on the driver's side.
In terms of breaking or slowing noise, you do hear it but I can't say it bugs me. I personally enjoy the HS because of its technology. It's a more intelligent car if you will and the hybrid noises remind me of it.
Now, while I've had my car for a year, I've recently just noticed that when slowing down after acceleration but not breaking, the sound that comes out of the hybrid system sometimes feels like an uneven wheel spinning. Don't know if it was there before but I just noticed it. Anybody know what I mean? Normal or my car needs servicing?