What Fugi said about volume settings.
For the reasons why, I've seen people hitting the tangent all of the time. Many of those have been either beginners or for other reasons just been taking out one plane after another, not bothering to answer to any questions about them needing help. One could even think they have the same button assigned to e.g. Teamspeak or for another function outside the game. Heck, they may even be some YouTube game vloggers using the tangent button for commenting how crappy the game is since they can't get the plane up!
I don't know if they're talking or what
No matter what the reason is, it can be very annoying. I've tried range speaking, range texting and PM's without any answer other than sometimes the guy changes the airfield and continues doing the same elsewhere. "Or what" seems to be the reason.