I was prone doing some random movements and had those message (broken leg) and inmediatelly died. The fact is that I was prone because I heared some sound of people walking and shots but there wasn't any person.

I think you should increase priority, it's really annoying because it's constant. I think what happens is that when a zombie plays a sound in other parts of the map the game client cant determine distance (or something relative to that) so it sounds like if it were next to it. Sometimes zombies doesn't make any sound.