better to fix the fault than just deal with the symptoms. Has the bike ever been in an accident? Something not quite straight? Fairing/bracket, fork alignment, front wheel - God forbid, frame not straight? Are the forks set up properly in the yokes - someone hasn't adjusted to alter steering speed/ride height?
My boxeye shakes its head at 30-45ish if you let go of the bars, its quite nasty really! I just simply keep hold of the bars and it stops Ill be investigating the cause of mine shortly, as I know its been in a crash. It was my sons bike before me, and he crashed it twice! It could be anything!