Unhappy [Q] During calls people on the other end can barely hear me (low, muffled voice)

I have an issue during phone calls: people on the other end can't hear me well: the voice is really low and muffled.

I have an international version (d802), stock software, rooted. Voice privacy was disabled by default and the enchancement option didn't help much (the suggested workarounds i've found). I see that many people have this issue, anyone has a proper solution?