Hello.
I have a project timeline (a short film of about 10 minutes) where a mysterious sound appears, although there is no audio clip active. There is a video clip, but it has no audio enabled. I can't get rid of the mysterious sound, although I have pasted everything into a clean new project, or even pasted it in parts, and putting the video clip anew from the Browser, but the mysterious sound keeps re-appearing (the sound sounds like some kind of weird slow-mo version of some sound, but it seems to have nothing to do with the video clip in place). I have also tried to crate a entirely new library, but the result is the same. And it does play on the audio bars and does appear when exporting as well. And I did delete all generated project files (render, optimized etc).
I even tried to export the video clip with no sound and re-imported it, but the mysterious sound keeps re-appearing.

Obviously a bug!?

Someone has an idea of how to get rid of this?

I'm running FCPX 10.3, but the same problem appeared in the previous version.

Here's some audio active:
https://youtu.be/NpFEoVUEhzI

It would help if you posted a framegrab from fcpx also showing the affected piece in the timeline and maybe let us hear what you are hearing? I don't have fcpx but I figured that you have a better chance in getting help if other fcpx owners can see and hear what is going on. I also doubt it's a bug if you experience the problem in 2 different versions.

If this odd audio is only associated with a particular clip where ever you place it on the timeline, regardless of the project you are working in, then there is something amiss with that clip. You can try to covert the clip to a different codec with Compressor (if you have it) or a free program like MPEGStreamclip. Exporting to the same codec, ProRes to ProRes for example, doesn't always recompress the clip depending if effects are applied or not.