Side mirror on ford Mustang?

My driver's side mirror (powered) on my 2000 Mustang vibrates when I drive. the housing of the mirror is fine it's not loose, it's the mirror itself. Does anyone know how to tighten the mirror inside the frame? Right know I have something wedge in there to keep it from vibrating when I drive. I have tried to moving the mirror left or right to see if I could see if there was any way I could look behind it to fit a screw driver or something to tighten it with ....no luck....help.