IMovie Voiceover recording

It would help if you could post a screen shot of what you are seeing in the timeline.

When you add a voiceover iMovie automatically lowers the volume of the main video clip above it so that the voiceover can be clearly heard. However, unless the video clip volume is very low to start with the voiceover shouldn't completely override it. Try selecting the voiceover clip by clicking on it, and then click on the loudspeaker item in the tool bar in the upper right of the screen. Uncheck the box that says "Lower volume of other clips{. See if that solves it.

You can also increase the volume of the video clip by selecting it and clicking on the loudspeaker icon and using the control slider that appears, to increase the volume of the upper clip. You can do the same to decrease the volume of the voiceover.

If none of the above works, try deleting preferences. Open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

You can also try creating a new project and see if the problem disappears there.

-- Rich

Great that you resolved it. Yes, it is strange that the reduce background noise tool would restore the sound. I wasn't able to replicate the issue on my system. But . . . whatever works, works. Nice job.

-- Rich