Malfunction Already??!?!?!

Hi Folks,

So I've put about 4000kms on my relatively new Prius and recently, I noticed a strange sound coming from the hood.

After the car is parked and I completely power it off, about 30sec to 1 minute later, I hear noises; sort of like electronic valves opening and closing / actuators from within the front engine bay. These noises last just a few seconds and then stop - I was used to this as I heard them since since the car was brand new, and the sounds were always consistent.

Then this last week, I heard the same sounds after the power-off of the car, followed by what sounded like a a loud "fart" noise. It sounded like whatever valves opening and closing needed to be lubricated because something i rubbing harder than it should be. The bad thing is that this "fart" noise which concerns me is never consistent. Some days I hear it, some days I don't.

First of all, does anyone know what happens under the hood when you power off the car? (why the strange noises?)

And on an unrelated issue, I am dying to know why everytime I open the drivers side car door to get in and go to work, the driver's door opening triggers a whirring noise coming from within the hood / underside. Opening other doors such as the passenger or rear doors does not initiate this noise.

Thanks folks!