Did you recently replace one of the motors?
I am having the exact same issue, and I did replace one.
Also, when the newer one closes, it makes a grinding sound for about 10 seconds.
My guess is that the arms and gears are not aligned, and/or there are broken teeth on the gear.
I plan to go to this guy for a fix:
http://www.bfranker.badz28.com/headlightfix/Expensive little part, but even after a few junkyard replacements, it's cheaper in the long run.
He also has instructions for aligning the actuator.