For a number of years, every time there's been an OS update, I've removed the extremely annoying "Volume Mount" sound at: /System/Library/Components/CoreAudio.component/Contents/SharedSupport/SystemSounds/system/Volume Mount.aif But when I attempt to delete that file in El Capitan, I get an error message: "The operation can't be deleted because the item "Volume Mount.aif" is locked. This was never a problem before. Things that didn't work: - Unlocking the file via the Get Info window. (Of course the numerous parent folders are also locked.) - Logging in as root. Honestly, I was confident that logging in as root would work, but it doesn't. Has Apple just locked down the system even further, this time? What must I now do to delete that frigging annoying sound?!?