Q: Sometimes it becomes quiet?

I used relative secure API so RetroKeyboard won't touch your key events when you types password, etc.

In rare cases, it will not play the keyboard sound at all suddenly. The only way I know to resolve was restarting the RetroKeyboard from System Preferences.

Q: Can I make my own keyboard profile?

Yes. You can reference files in RetroKeyboard.prefPane/Contents/Resources/Profiles. Record your sound files and make a Mapping.plist. The array index in Mapping.plist represents keycode of each key. keycode