Does your iPhone mysteriously vibrate in your pocket? Mine started doing so more and more till I discovered that something was wrong with my iPhone.
First thing to check is whether you have received emails or push notifications as these will cause your phone to vibrate. Unless like me your phone is broken, an app on your phone will cause it to vibrate.
For me I found that my phone was vibrating in my pocket and would continuously vibrate in an inconsistent pattern.
After checking my phone many times I found that if I squeezed my phone from the front and back on the top left of the iPhone (silent switch area) it would vibrate. It would only do this if the phone was set to silent. So if I kept squeezing the phone I could get it to constantly vibrate.
An appointment at the Genius bar in the Apple store was booked. After showing them the issue the iPhone was swapped for a new/refurbished one, without an issue. As expected the genius came to the conclusion that the connection to the switch must have been dodgy. However he had not seen the issue before.
I am posting this after a few people have hit my site by searching for answers to the mystery vibrating of their iPhones. Maybe the above is what your experiencing. Hopefully this will help someone out there.