Yes, it is! The `click' is the sound of the aperture diaphragm closing to the chosen f-stop value.
Except in manual mode, the diaphragm is opened to f2.8, the maximum aperture diameter, if the shutter button is not depressed (pushed). This is to allow the maximum light to enter the camera, giving the brightest possible image in the viewfinder. However, if the camera thinks f2.8 is not the best aperture to use when the picture is being taken (this is usually the case if the ambient light is bright e.g. outdoors with bright sunlight), it will reduce the aperture when the picture is taken (i.e. the shutter button is fully depressed). The makers of the FZ10 (Panasonic) have also decided to reduce the shutter aperture when the shutter button is half-depressed, to give a preview through the viewfinder of what the picture will eventually look like (darker, and with increased depth of field).
Unfortunately, both the darker image and increased depth of field are misleading. Long shutter times can make the eventual recorded image much brighter than appears in the viewfinder. The low resolution of the electronic viewfinder or LCD display make depth of field (the range of distances from the camera at which objects are sharply focussed) difficult to judge.
You can actually see the aperture diaphragm closing to a smaller diameter (which is, paradoxically, a larger f-stop number) if you are in bright light and look through the lens towards the back of the camera and half-depress the shutter release button.
The click does not happen in manual exposure mode. This is because Panasonic has chosen to close the diaphragm to the manually chosen aperture at all times, even if the shutter button is not half-depressed (this is the source of complaints from FZ10 users, see Section ). If you set the camera to manual exposure mode, you can hear the `click' each time the aperture is changed. If you look down the lens, you can see the diaphragm diameter change each time the aperture is changed.