the vibration can't be caused bu too much head speed, actually when you increase head speed, vibrations usually get better. Oh and why is it bad to spin up your heli without blades? I've never heard such a thing, If you did then its probably true if you slam the stick to full power because you WILL damage something because of the rpms, but if you just spin it up to about 50% power then you won't have any problems, and besides it can't be worst than spinning it with a vibration. If you can't find the problem I really suggest you look for it this way because maybe its not even coming from the blades but from bearing or some bent shaft that can cost you the heli later down the road.