With a quick trip to Terminal, it’s fairly easy to replace the volume changing sound with one of your own choice. Note that you can do this in the Finder, but it requires modifying the permissions on a file (or folder)—and since it’s Geeky Friday anyway, I chose to show the Terminal solution. Start by finding a sound you want to use—it should be very short, and must be in AIFF format. (iTunes, or any one of a number of programs, can be used to convert sounds to AIFF format if need be.) Put the file on your Desktop for easy access.
Open Terminal, and navigate into the folder that contains the volume changing click noise:
cd /System/Library/LoginPlugins/BezelServices.loginPlugin/Contents/Resources If you then do an ls, you’ll see a file named volume.aiff. That’s the file you need to replace with the sound you’d like to use. First, though, create a backup of the original:
sudo cp volume.aiff volume_backup.aiff Provide your password when prompted, and you now have a backup copy of the original file, in case you want to revert your changes at some point. Now all you need to do is copy in the sound file you found earlier, and placed on your Desktop:
sudo cp "~/Desktop/mysound.aiff" volume.aiff Replace mysound.aiff with the name of your actual sound file, of course. When you’re done, if you do an ls -al, you’ll see volume.aiff (your new sound file) and volume_backup.aiff (the original). Because you used Terminal, you shouldn’t have to worry about permissions—note that both volume files show identical permissions in the directory listing you just ran.
The last step is to restart—after that, your new sound effect should be heard whenever you change the volume via the keyboard. If you ever tire of your new sound, just open Terminal again, cd to the same directory as before, and then run this command:
sudo cp volume_backup.aiff volume.aiff Restart again, and all should be back to normal. As with any hint that modifies your file system, however, there is no warranty expressed or implied—this particular tip hasn’t given me any trouble, but there’s always the chance for a minor disaster when you’re modifying files in system folders.