I have the same issue; however, I know my phone was not doing this until today. The dual vibrate is obvious & annoying; I am pretty sure I would have noticed it. Make it go away! I am set to off on both settings, yet it still does the dual vibrate when connecting to the charger now.
If you mean the vibrating when you put it into the dock or connect it to the charger, you can't change that, it is activated by default. But it should only do this when you connect it for the first time, not during the charging process. If it vibrates while charging, check your connections and cables.