Do you have Vegasaur installed, which has a render assistant that tells you by a female voice that the render has completed? Vegas itself doesn't have a voice telling you that the render has completed.
@3POINT ... yes, it's Vegasaur. I've been trying to think how I changed years ago the "rendering complete" to another sound, and you've hit the nail on the head.
In C:\Progam Files\Vegasaur\[version number]\Sounds, the source for the rendering complete alert is 'rendercomplete.wav'. What I did was removed the above wav file and took another .wav sound effect and renamed it 'rendercomplete.wav' and put it into the Sounds folder. Think I'll do that again right away.