Unhappy [Q] Jiayu G4 - phone call problem

Hello to everyone and have a happy new year,
i bought a Jiayu G4 phone a month ago and i face a problem in calling. When i am on a phone call, the person to the other side of the call hears a noise. This noise, to help you understand, it's similar to the sound that a TV or THE SPEAKERS do when you put a mobile phone near them. This is very annoying and i can't explain why it happens. Now, in order to make the things better till i'll find a solution, i bought a bluetooth. The problem whem i'm using it, is that the person to the other side of the call can't hear me correctly. To help you understand, my voice it's like a robot's voice and it's not quite loud. Does anyone have an idea how to face that?

Thanks a lot