The thing that you are speaking is for auto-focus (AF) but not for the control of the aperture lever.
If you snap your shutter without a lens on, you'll see that the lever will snap down before your mirror will flip up then close. This is to stop down the aperture to what you've indicated for your shot.
Both will constitute to the loud sounds that you're hearing.
I'm not as bothered with the sound as with the vibration that I'm experiencing though I'd love for it to be much softer.
You can consider to change to Canon or to a rangefinder if you think that this is making you peeved.