Random vibration notification?

[rtb]

A couple of times a day my Moto X just vibrates loud one time for no reason.
There's no notification on the phone. Anyone else have this or know how to
fix?

 

[TatDroid]

Sorry, that's a new one on me.

 

[Snoking]

Is it at 11pm and 6am. Wife's X defaulted to sleep from 11-6. Maybe it is notifying about that. Chris