Funny you should ask. I came across a program that lets you do this while I was searching for something else on the forum today. I think it was something like sythesize text to speech or something like that. The reason I don't know exactly was because it will download and install, then delete the install files and leave no trace that it was installed other than voice is now working. Maybe someone else can remember what it is called.

 

Try, Settings/Text to Speech/Install Voice Data

 

i thought the same thing until today. at first i just put in a address and nothing happen just got the route info. then this morning i thought i would try it again. i didnt hear a voice until i started driving. maybe not the case with you. and i also had i had to install some voice feat. but it asked to install so it would work. or maybe the navi volume isnt turned up. dunno hope this helps.

 

My volume wasn't turned up, lol works fine for me