One of my teachers used to tell me that there were three stages to learning to do something new. First, you can't do it. Then you can do it badly, and finally you can do it well! Obviously, that's a little tongue in cheek, but the theory is right. It sounds like you're into a new part of the register, and are probably in the second stage...that's good! Give it some time, practice up there a little and let the squeaky sounds grow into bigger sounds. Where there's smoke, there's fire!