I have a laaaaaaaaaarge project shot with two cameras that I've been editing as multiclip. Everything worked as usual, until yesterday, when I tried to switch angles in one of the cuts, I just got a "cling" from the Mac's speaker, and nothing happened. I tried collapsing and uncollapsing the clips, and nothing happened. Protecting the audio tracks, and nothing happened...

What's going wrong with that d*$%#d thing?

multiclip goes wonky if its rendered in the timeline ... make sure your multiclip is unrendered

Thank you, Andy. I have solved the problem. On the Viewer window, there are three buttons between the two timecode displays. On the central one, the line "Video + Audio" or "Video" must be checked. If not, it's impossible to change the active angle.