I think the usual cause of this is corrosion inside the power door lock unit.
 There are contacts inside that act as switches.  When you pull up on one
lock it acts as a switch to activate the others.  The motors run until they
turn the little wheels inside to hit the next position and that shuts them
off.  If the contacts inside get too corroded the motors will turn until they
get to the next spot, but then there is no contact, so it malfunctions and
moves back in the other direction again until it hits the contact and stops.
The only way to fix this is to either open up the motor and attempt to clean
it (not easy), or to replace with a known good or new unit.
I have new power lock motors for the rear hatch and sliding door for $60 each.
The new front door lock motors are $70 each (one of these is the culprit).
Let me know if I can help you.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16
Office (856)-765-1583
Shop (856)-327-0027
Fax   (856)-327-2242