Mine was really annoying, full up at slow speeds it shook and rattled audibly, not so much in the down position. I removed the shield, front cover and looked at the mechanism. There is a flat guide the support "grips" to hold the traveler as it goes up/down. There is a white nylon "clip" that acts as a bearing/guide and it has apparently lost some elasticity and was not gripping the flat guide bar. I shimmed under the inside half of the clip about .020" so it actually grips the flat guide, cleaned and lubed both sides of the flat guide bar and it tightened everything up nicely. I have a Cee-Baily ultra-tour which is quite tall and this exagerates the wiggle.
Thanks!