It's definitely the Immersive Spatial Audio. I installed the trial to check after trying all other "fixes" I'd found online and the stuttering stopped. Sadly though now everything sounds just awful. I have no idea what that program does but using it makes everything sound like I'm playing underwater

Playing in DX9 helps the sound a lot for me but it also makes my game crash and freeze in busy areas. I really hope this gets sorted soon as it's really damaging my experience with EW