LG B2 55" Optical Out makes terrible crackling noise

So I know it's not the optical cable as it's new and a decent cable. I also know it's not an optical cable issue as when I put the setting in optical + TV it works fine. I mute the TV and it works I'm assuming as it should. But when I put the setting to optical out only, it makes a terrible sound. Can't find any information on this. Any ideas or thoughts?