I played on a friend's partscaster strat recently & when playing I was able to move the neck slightly without much force. When I checked the screws seemed fairly tight and/or proper tension. I didn't want to over tighten them... When moved the alignment would change. -Push downward and the strings are closer to the unwound E string. -Pull upward and the strings are closer to the wound E. What would cause this and can it be fixed?