Final Cut Pro Playing Random Audio? Here's the Fix

You're playing back your timeline and there's audio you can't see anywhere. No audio track, no obvious clip, just sound appearing out of nowhere. This happens for two different reasons, and both have quick fixes.

Fix 1: The Invisible L-Cut

The most common cause. You cut a video clip shorter, but the audio from that same clip is still extending past where the video ends. It's just hidden underneath other clips. Select a clip near where the mystery audio starts, then press ⌃S to expand the audio and video separately. If the audio waveform is extending past the video portion of the clip, that's your culprit. It's technically an L-cut (audio continues after the video cuts away).

Fix 2: Ghost Audio Track in the Index

The weirder one. You expand every surrounding clip and find nothing. The audio that's playing isn't attached to any visible clip and seems to be coming from somewhere else in the timeline entirely. This is what Dylan calls a "ghost" audio track.

Open the Timeline Index by clicking the icon in the top left of the timeline window. Switch to the Audio tab so only audio clips are shown. Then find the approximate timecode where the mystery audio begins playing, and look for any audio track in the index that seems out of place, positioned too early or too late compared to where you'd expect it.

When you click a track in the index, it also selects that clip wherever it's sitting on your timeline. If you see it get selected but you can't find it on screen, that ghost track is buried somewhere. With it selected in the index, just press Delete to remove it.