My Microsoft Lumia 640 has a sound problem that affects the in-call sound. It does it with the earpiece, headphone jack and speaker. A factory reset didn't fix it and the sim works fine in an old payg phone.
When in a call the sound fades out every second so I only get half the conversation. Virgin support want me to send it back for repair which means it goes to Hungary for goodness knows long. I'm not happy with that fix as I doubt I will hear anything for some weeks leaving me with no phone.
Have you heard of such problems? Google search came back blank.