well because many people have a common problem with the umd drive when they change the backplate to a 3rd party one, this is common on the phat though. maybe you might have the same problem that the gears arent moving freely because of part of the backplate obstructing it but as i said that was on the phat, im not sure if the slim has this problem. or check if theres like some dirt or a hair obstructing the drive from operating properly?