Is there no sound at all?
Check if device's setting for 'Media volume' is turned up as the volume slider in Waze does not sync with that.

Ensure that Settings/Sound/Level of guidance is set to Including street names.

Sent from my HTC Sensation Z710e using Tapatalk 2

Which devices?
It might be worth a check in Settings / Sound to verify that Navigation is set to full and volume slider is al the way up.
You can also check if forcing 'route to speaker' helps in your case.
iOS also has a prefer bluetooth setting that might interfere.
Main menu mute icon should also indicate if mute is active.

Sent from my HTC Sensation Z710e using Tapatalk 2

The app has its own mute button in the menu...umm the non report menu above navigation in android... - looks like a speaker as you would expect - this caught me also...

after updating to 3.6.0 version with downloaded correct sounds I also have got same problem - now im without sound

I tried to change sound level, mute/unmute main sound+app waze mute/unmute, check/uncheck preference box for output, reinstaled waze and still Im in silence.
I already restarted app and phone many times - of course.

Device is Huawei Ascend G300 with android 2.3.6.

(Main mute button I also tried check/uncheck more than ten times..)

Maybe reason for this could be that i never catch first appearance of ask for downloading additional sound/languge files during initial settings of Waze. I always have to wait to next start of waze and after this i get again this ask? I always miss original first appearance because there is terrible placement of first use video which is for me on top of the all dialogs.