The lenses with an internal focus mechanism generally featured lower noise, with the Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro and Lumix G HD 14-140mm f/4-5.8 as exceptions. In the latter case, I believe the microphone was too close to the lens, giving biased results.
You could ask why worry about the aperture change noise. After all, the aperture is generally stopped down just before the shutter is released. And for all Micro Four Thirds cameras, the shutter noise is rather high. So the aperture noise is simply drowned by the shutter noise anyway.
However, there are times when you don't trigger the shutter. This could be when using the new high speed, low resolution mode of the Panasonic GH2. Or, quite simply, when recording videos.
Also, some time in the future, we are going to get cameras without mechanical shutters. When the global shutter technology is mature enough, we will see this in Micro Four Thirds cameras. Then, the only noise we will hear is the focus noise and aperture noise.
To measure the aperture change noise, I placed a mobile phone near the camera, running the "Decibel Ultra" app, to measure the noise level. While I don't trust the absolute measurement of the phone, I think it is good enough to look at the relative levels of noise.
The GH2, and many other Micro Four Thirds cameras, has the feature of stopping down the aperture to preview the depth of focus (DOF). This is very useful, especially for macro photography. I use this feature to toggle the aperture between maximum and f/7.1.
I have only noted down the peak decibel measurements. The results:
Lumix G 8mm fisheye
|77 76 77||77 dB|
|Lumix G 14mm||79 77||78 dB|
|Lumix G 20mm||76 75 73 76||75 dB|
|Leica Lumix DG 45mm macro||80 82 81 83||82 dB|
|Lumix G 45-200||83 80 81 84 83||82 dB|
|Lumix G 14-42||75 76 75 75||75 dB|
|Lumix G HD 14-140||78 78 81||79 dB|
According to the marketing material, the HD designation of the Lumix G HD 14-140mm f/4-5.8 superzoom lens means that it should have fast autofocus, low noise autofocus, and near stepless low noise aperture.
After my analysis of the AF speed, the AF noise and now, the aperture noise, I cannot see that the lens is that special. It performs pretty much like the basic kit lens. What I haven't looked at, though is the aperture change, which is quoted as "near stepless". Accurate to 1/6 stop, is what I have seen quoted.
That said, the Lumix G HD 14-140mm f/4-5.8 zoom lens does have a softer sound when changing aperture.
In terms of aperture noise, the lenses appear to perform quite similar. And this is not strange: The aperture diaphragm mechanisms are probably rather similar between the lenses.