Thanks to these two posts: -
I now have the "old" blobby-clicky sound when I increase/decrease the volume on OS X Yosemite.
In essence, the first link includes a .AIFF file with which one replaces the default ( and new ) sounds, setting it back to pre-Yosemite.
In addition, it also shows one how to change the System Preferences to ensure that the sound is heard when pressing [Volume Up] and [Volume Down], rather than the ( now default ) shifted versions of those keys.
It's all good.