Found this on MacRumors - if all your settings are correct on Waze (sound on, play through phone speaker, volume slider at max) and your iPhone volume is at max and you hear no (or very low) voice guidance - set a destination, go now, and when the voice guidance starts, press the up volume on your phone (even though it showed at max volume!) - this weird solution worked for me and several others. I have a feeling that if you are trying to play on a car sound system (and have selected the option in the Waze app) Ithis solution might work there too, though I haven't tried it yet..... I was going crazy looking for solutions, deleted and reinstalled the app, cleared caches repeatedly, and spent way too long with Waze support! Hope it works for you too.