For a projector to run right, the motor has gear teeth in it that engage with the hollow points on the film itself. The motor has to turn at a steady speed with no friction or hesitation. It is possible the motor on the inside of the projector needs to be oiled or cleaned out...or rebuilt at worse.
There is also the motor that pulls the film thru the projector and winds it onto the receiving spool. Sometimes that motor is out of synch with the projector drive motor and trys to pull the film thru to fast or turns to slow and the you get that "clicking " sound when the receiving spool isn't winding the film up fast enough and the film gets dragged on by those projector teeth and make that plastic clicking sound.
Watch the film while it is running between the two reels and the projector lens. The film should be slightly taunt going into the projector and slightly taunt coming back out of the projector. If you see the film grouping up in front of the projector drive or after, then you know your spools are needing greased up or there is a drag on the motors causing things to be unsynchronized.

This is definitely a mechanical problem and you need to watch the film being fed into the projector and how it is wound up n the receiver spool to see where the fault lies.