I always keep my cell phone in my left pant pocket. Every now and then I will have a muscle spasm or some kind of vibration in my leg when my phone isn't ringing. It is similar (but not identical) to the feeling I get when my phone rings. I'm curious what is causing this. Is it a muscle memory sort of thing or are there waves being emitted by the phone that are now causing my quadraceps to go crazy?

It certainly doesn't hurt and isn't an issue, but I'm curious. Any thoughts or should I bring this to Ask Metafilter?