Hi, so I just upgraded to the OS X El Capitan Beta and it's not bad but I'm having one problem. In Yosemite I changed the volume sound back to the original on from Mavericks and every other OS X before it. I tried to do the same thing once I upgraded to El Capitan but it won't let me. No matter what commands I use it just says "Operation not permitted" Things I've tried: Just deleting it using finder. Result: The operation can’t be completed because the item “volume.aiff” is locked. In terminal : cd /System/Library/LoginPlugins/BezelServices.loginPlugin/Contents/Resources sudo cp volume.iff volume_backup.aiff. Result: Operation not allowed sudo chown Michael /System/Library/LoginPlugins/BezelServices.loginPlugin/Contents/Resources Result: Operation not allowed. I'm really not sure what else to try but I hate the default volume changing sound in Yosemite and El Capitan. I also tried changing the permissions by pressing Command & i but it just says I don't have permission to do that.