From 24-50 is OK, but from 50-70 or 70-50 it will have some vibration and noise. The lens is still useable now but would like to repair it. Compare mine with my friends 24-70, my zoom ring is definitely stiffer. I normally transportation the lens with the Hood reverse.
As time goes by the stiff will get worst and eventually u'll have a NIKON AF 24-50 2.8G... :bsmilie: