I just upgraded my MacBook to Yosemite, and the new sound effect for the volume button is just awful. Is there a way to change out the sound file so I can hear the old version on Yosemite?
It can be done, although you need to find the Mavericks volume feedback sound file. The filename is "volume.aiff" and (for both Mavericks and Yosemite) it is located in: /System/Library/LoginPlugins/BezelServices.loginPlugin/Contents/Resources
Find the Mavericks volume feedback sound file and put it on your Desktop for easy access.
Open the Terminal and navigate to the folder containing the sound file:
Create a backup of the original file in case you want to reverse the changes:
sudo cp volume.aiff volume.aiff.bak
Provide the password when prompted.
Now copy in the Mavericks sound file placed on your Desktop:
sudo cp ~/Desktop/volume.aiff ./
This works perfectly AFTER you boot into recovery (by holding CMD+R at boot up).
From there open Terminal (under the Utilities menu) and enter
csrutil disable (to disable System Integrity Protection).
Once you do that there are no issues though I would recommend you repeat the above process when done and enter
csrutil enable into Terminal to enable System Integrity Protection.