I have to admit I didn't even know that whatsapp allows voice notes. But I do find it weird that you want yappari to play voice notes when the user has explicitly set the phone to be silent.

I just hope you're doing this because you anyway need user interaction in order to play a voice note (in which case it would make sense). If the voice notes are played automatically without user interaction then I hope there's a way to deactivate it. In simple words: I don't want spam coming out of my pocket