Just started doing this recently, but in the middle of typing a text/email, the haptic feedback from typing stops. Also, I don't get the feedback when using the 4 main buttons on the bottom. I notice when the feedback stops, the vibrate feature also stops. I can shake the phone a little bit, then it comes back for a while, then it goes away again.
I haven't dropped it (at least that I can recall), and I've had an Otterbox on it since day one. Has anyone else had issues with this? I'm probably going to take it to a store and have the phone replaced.