My Nikon D40 is making a noise when the shutter is half depressed. Is this normal?

When I half depress the shutter button a sound like something is spinning on the inside. It doesn't turn off right away when I undepress the shutter. Is this normal?

Yes i think it's just it focusing my old kodak did the same thing, heck every camera i ever had would make this noise when you half press the button

It's the autofocus at work

That's true but not only the focus but also the aperture is setting the exposure… All normal sounds.

More likely the lens than the body. Could be the autofocus, could be the lens VR.