Rear side door makes loud buzzing/grinding noise when locked. When unlocked, no noise. Only when locking.

 

Sounds like the door lock solenoid is bad or sticking.

Best thing to do is take door panel off and watch the action of the solenoid and see if anything is binding. If not might need a new door lock solenoid.

Good luck

 

Thanks. Kind of hard to see. Its behind the steal. I will get someone to look through. Thanks