Well, this is weird.
I don't know what I did, but the problem seems to have gone away! I've changed a few things, such as run with vsync on, max fps off, put PC in Ultra Performance mode (which I didn't know existed!) and the sound stuttering has completely gone away! Even with Dolby Atmos off. However, when I put the settings back to where they were, it still seems to be fine. God knows why, I've not changed any drivers or anything like that, very weird.
Anyway, I'm happy now. Seems to be fine for now.
Cheers 👍