Check your project file. I’ve seen this problem with projects that are in 59.94. Change it to 60fps and the sound is no longer there.
Not sure if that helps, but by your description it sounded similar.
I've encountered a sound bug several times on multiple projects that makes it difficult to work in Luma.
Often when adding b-roll in video track 2 or 3 and muting it, there will still be be sound in the first frame or two of the b-roll clip.
I've read about the issue before, but there seems to be no fix.
Anybody encountered this and know how to fix it?
Thanks in advance!