I hope this isn’t by design?
Not even a re-import/re-serialize could remove it. It’s as if the AudioTrack was a subasset and just remains forever.
Which also raises the question. Is this the case for any Timeline track?
Maybe some utility is needed: “Remove Unused Tracks” which searches the sub assets and deletes ones that aren’t directly referenced by the Timeline
The tracks are sub-assets. There’s no real way around it with ScriptableObjects, they need to belong to an asset file on-disk.
But removing tracks is supposed to remove them from the asset.
Without knowing what manipulations led to this, it’s a bit hard to fix it automatically. We could do a check in OnValidate to check that there are no unreferenced tracks, but that would kill edition performance for anyone that has a large-ish Timeline.
Similarly with a warning in the Inspector.
But we could probably add a button in the Timeline Inspector that does a wide sweep of tracks and clips, and compares the list of sub-assets to validate that they are all referenced.