As it reads sometimes the gear is not broken, even if it will break soon, they all are.
And as the clickings is constant it can't be the gear giving the sound as the gear only moves every now and then,
the only thing moving all the time is the disc, meaning it's someting with the motor for it, the holder for it could have gotten pressed
down to much on it's axel, making woobly discs hit/scratch something while spinning, the holder (spindle?) can be pressed up if that
were the problem.
The motor for the cd could be on it's last leg... extremely unusal but, could be something physical in it, perhaps...