RE: Let me get this straight ! [8|]
Its highly unlikely that its the tranny voltage. I have a 9Z and used to have a 9c use liion in them and when fully charged they will show 12V with no troubles. Like wise with the receiver Futaba says theirs can take way more than 7v. Servos will dance and then settle down with a unregulated 6v system as the battery settles.
You can swamp a system by transmitting to close to the plane.
Like the previous poster said try it a little distance away and see if it does it.