I have a problem with 1 of the door power locks on my car. It's the rear driver's side door. When I go lock all the doors sometimes I will hear a different noise and the rear driver's side door lock won't go down. It is very erratic though, and I can't figure out why it goes down sometimes and why it doesn't Any suggestions? Is the power door lock somethign I could easily replace myself?

 

Search "door lock actuator" in my signature. I'm sure you'll find many results.

 

It is probably the actuator. Not too hard to fix, but you have to take the door apart which is a real pain. The only thing that may be hard is actually accessing the actuator to replace it (if it's broken - you need to test it first.)