I think a simple setting has become modified.
Are you using Phatnoise Media Manager or Music Manager?
In Media Manager (not sure about Music Manager), look in the menus under Tools, Options, General, Voice prompts.
There is a slider to control the speed of the speech - enter a test message to hear the effect of changing speed.
Once you have played with this and have it as you like, you will need to delete the TTS folder on your DMS, and the next time that you do a Save and Eject, the TTS folder will be recreated with new voices according to the settings that you have selected.
Good luck!