Sounds like the lock motor is starting to go. It has plastic gears in it and as they wear/break it starts to work sometimes, sometimes not. Mine did this (drivers side). Then it stopped working completely. I got my motor from OCWILEY who is parting his out. He may still have the passenger side motor. Drop him a line. Price and service were great. Its a pretty easy replacement process. Takes about 45 minutes and a phillips screw driver. Just be carefull with the little plastic connectors on the rods. They are fragile. If you have any ????'s just give me a holler. (I just replaced it this weekend).