[Mattheyu]

I've run into the same issue on multiple ROMs on the Titan and my TP. It normally only happens to me when I receive a text message while I'm doing something else on my phone such as in a call or playing a game.

Easiest way to stop it is to open Sounds and Notifications in Settings, and disable vibrate for text messages and it immediately stops after I exit. I just go back in and re-enable it afterwards.