Originally Posted by bakntyme

Do you have low battery when it vibrates? It could be the low battery warning, I think mine vibrates from that even when the phone is set to complete silence.

Does it randomly vibrate if you hard reset and do not load any programs or data on the phone? If not, one of your programs or settings or datum is causing it. Load your calendar, then one program at a time until it starts happening.

Or maybe your phone is just shivering from the cold weather there in Colorado.