2000 300M power lock makes noise

The power lock in rear passenger side door makes a loud screeching noise whenever you lock it with remote or going over 15 mph. Is the solenoid going bad or the relay switch? This is something that I can be able to replace parts for myself instead of going to the B.S. 5 stars dealership. Help is much appreciated. Thanks.

ha ha the duck in the door very common on the lhs,concorde and 300m all you need in is the door latch accuator it is a tricky job to do because of the door rods are attached to it just very little room to work. but it is fairy easy