Some comments are going around online regarding the audible clicks that are heard while zooming with the Panasonic 12-35mm f/2.8 lens.
I even had one stranger messaging me about that.
Mine does that too, on a Panasonic GH2. Slightly on the A and S mode, and more frequently with the video mode.
A Panasonic camera will adjust the aperture blades to varying amount of light to give a well exposed image on the LCD screen. The keyword in the previous sentence is blades. When you press the shutter, you will get the aperture that's shown on the LCD screen.
Olympus cameras will, if I'm not wrong, adjust the aperture whenever possible giving the clicking sound constantly.
Here are two interesting tests to try.
In the first test, set your camera to Aperture mode at f/2.8, zoom to 12mm, and hit the Shutter Effect button. Look at the aperture blades as you zoom slowly to 35mm. You should notice the blades close down by 3 clicks, or 1 stop, but the LCD is still showing f/2.8.
In the second test, at either 12mm and 35mm, press the Shutter Effect button and count the number of clicks you get to f/22. They should be the same.
This tells us that at 35mm, to achieve f/2.8, the aperture blades have to open wide all the way. And at 12mm to achieve f/2.8, the blades have to close down by 3 clicks.
So the f/2.8 is still constant throughout the zoom. The clicking is there for a reason.
On a more important note, the clicking might actually cause flicker when you're in video mode.