ANDROID Voices too quiet...

I can barely hear the GB TTS voices in Navigon 8.5.2 (I'm using a Moto G4 with Nougat)! Sound output on this phone is fine in all other respects...

I REALLY like Navigon, but this is a deal breaker for me :buu:

Does anybody else here have this problem? Are there any solutions?

Cheers everybody!
Oi