maybe the tracking is off.
why the tracking is off could be because the brain that controls it is dead or dieing.
sometimes you can shove the tracks yourself and hope the controller allows it all to work properly.
maybe the controller is okay but there is a problem with the reset function.
most of the calibration process is done every time a disc is inserted because you never know when or who has bumped the laser and thrown off the calibration.
so it is supposed to go into its little corner and tell itself 'this is default.. now go to the spot you remember'
and if there is a problem with the processing of 'this is default'
then the track could go on and on until a timeout is reached.. and it is the gears trying to make the laser move in one direction, but the laser is already as far to that direction as it can go.
the clicking is the gear jumping as it spins on the lubrication and tries to force the other gear to move.
the second gear isnt going anywhere with the laser at the edge already.
i would assume this is an IC problem.. either the IC chip is not getting enough voltage, or the chip itself has gone bad because of age.