Apple iPod allows setting maximum volume limit with support for PIN code locking to prevent unauthorized changes, However, if you forgot your volume limit unlock code here is a little trick you can use to remove the lock without restoring your iPod.
- Connect your iPod to your computer.
- Make sure you have enabled viewing of Hidden files and folders in Windows Explorer, if not Open Windows Explorer -> Tools (Menu)-> Folder Options -> View -> Show hidden files and folders.
- Open "My Computer" and navigate to folder "iPod_Control" and then go to "Device" folder.
- Delete the file _volumelocked located inside "Device" folder (See image below).
- Now, Eject your iPod and restart it using the instructions provided here.
- You can now change the iPod Volume limit without unlock code by navigating to Settings -> Volume Limit on your device.
Note : As mentioned in the comments, you need to enable "show hidden files" option in Windows explorer to see the folder.