I don’t think it is software, it looks like either like @ben suggests, sim card, or the FP3 itself.
You should try with another sim card, the one of a friend or whatever, and then contact the support service :-/
Also you can try to go in developer’s options (click several times on build information in about this phone, in parameters), then the last entrie called Service Meu, then perform related test to sound maybe.