Have you performed any maintenance to this machine prior to this happening?
What kind of blades?
Does this only happen on the ground or in flight/hover?
When you turn the primary system off, does the blade track change at all?
With the Primary system off, can you see or feel any of the controls moving between the rotor head and the aux pack?
Checked the pitch horn eye bolts, swashplate, uniball and both scissors?