A friend sent a link of a close lightning strike near Darwin, Australia captured yesterday (12/25/10). You can hear an audible snap during (or very close after) the bright return stroke and prior to the thunder reaching them. This was likely a short upward leader that was very close to them that failed to connect with the downward moving leader. The snap is weak thunder that is created by the short and much less energetic upward leader that fails to connect. Given that you can hear it and that it is so close to the return stroke in time means that it was extremely close to the cameras. If it had connected, the return stroke would have likely have been within a few meters of the photographers.
There appears to be a barbed wire fence in the foreground near the tripods. Another possibility is that the snap is a short spark or audible corona or current flow that was induced in the fence by the nearby flash. I have heard this when filming near powerlines, but this usually sounds more like a zipper or buzz rather than a snap.
It is also very interesting to see the puff of smoke or dirt that kicks up where the connection is made.
Here is a direct link to the YouTube video.
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