We have received reports of a "clicking" sound which may be heard in the audio playback of movies recorded by the NEX-5N camera. This phenomenon occurs if the camera undergoes sudden motion while recording; motion generally inconsistent with smooth video recording.
The video is unaffected by this sound. In accordance with Sony's policy of continuous product improvement, an adjustment has been developed to reduce the clicking sound resulting from sudden motion during movie recording.
Sony will offer this performance improvement to NEX-5N end users during the period of its limited warranty accompanying the product. Please call 888-868-7392 to arrange for this improvement.
In other words, while your camera is still under warranty, take it in, and they'll fix the problem.
According to Imaging-Resource, Sony is now installing the fix at the point of production, so it shouldn't be an issue with cameras bought in the future.
We do wish that Sony would have mentioned the cause of the problem, if only to answer our own curiousity about what precisely was causing that clicking noise — our money's still on the image stabilization system.