not counting tours and such, it only has happened once, and it was the creepiest thing. I was trying out a 30 mile loop, suddenly I hear a 'hello'. no sound, nothing. just the word 'hello' then suddenly two cyclist zoom right past me. Had they not spoken a greeting, I wouldn't have heard them at all. Within minutes, I couldn't see them anymore. I had never had that happen to me before, it was darn creepy.