It could just be rubbing/hung on something inside the door. I thought my driver side was shoot until I took the panel off to change the speakers, turns out there was over $4 in change in the door (not counting the pennies [&:]) and it was causing problems. Try taking the panel off the door, and try the locks then, if it still makes a noise, you can trace it a lot easier. There's a good site that walks you through taking the door off for speaker replacement, but it should work for you too.
Passenger front door look makes a Funky noise
