My '03 F-150 passenger door "growls" every time the doors lock. Is there a gear on the lock solenoid that could be stripped out or something?

 

The lock actuator is actually a reversable DC motor.
It turns a 'fast' Helix to drive either pull down or push up the link to the lock hardware.
It has a boot over it to keep water out of the motor and drive.
If the boot fails the water will rust the drive and freeze in the motor.
Good luck.

 

Thanks, Bluegrass 7. I'll pull the door apart and check it out.