This happens to me when I'm driving. I swear I feel the thing buzzing in my pocket.
Yea I just assume anyone who keeps their cellphone on vibrate for any length of time (~1 year straight) gets that.
And I'm 100% positive it has to do with your body subconsciously picking up on the cell phone signal. Because when I got my new smart phone over my dumb phone, the smart phone throws out way more signal, which I knew about.
But it felt like I was constantly getting a call, especially while driving and there was a burst of signal as it changed between towers etc.
Instead of "buzz buzz" which was always accurate on my old phone (phantom vibrate when it was on silent, actually getting a call anyway) the smart phone was like "buz... buz.. bu..... buz..... buzzzzzzz..... buz.... bu..... buz." to the extent that its actually annoying and I don't carry it in my pocket much.
AFAIK its just your brain playing tricks on you. It senses the burst of cell signal that normally indicates a call and you'll hallucinate vibrate or your ringtone.