Skimming in the new iMovie is really cool and creating a video with it is much faster. The only thing that I find really annoying about skimming with video is the sound. At the speed you are watching the video when skimming, the sound is basically useless. There is thankfully a way to disable the sound skimming. The feature will continue to work in the same way, but without the annoying sound. To disable it, go to the "View" menu and disable "Audio Skimming". You can do the same with "Command-K".