Moved from another post, thought maybe no one saw it as there were no responses to this particular question. I noticed today, when stopped at a light I could hear the electric motor for the brakes...
I believe the later model units did away with the power steering pump and only use the electric pump, which is why you hear it all the time, regardless of if the engine is running or not. My parents W22 runs the pump any time you press the brake, regardless of if the engine is running or not.