I'm afraid that's the classic noise of a common fault! The magnetic ring for the FG servo is just above the commutator and when the plastic “tyre” that holds it in place cracks, the loose end gets mixed up with the brushes and makes a noise. Normally just removing the offending loose piece is all you have to do, the ring seems to stay in place by itself. To do this you have to remove the bottom of the motor, unsolder the PCB and then take off the brush plate. It is much easier to put it back together if you take the pulley off first, then you can insert the rotor into the brush plate before sliding the complete assembly into the stator. Be sure not to lose any of the spacers and washers on the motor shaft, their positions are important. A tiny spot of oil on the two bearings is also a good idea while it is in pieces. If that sounds all too scary, though, another motor from a turntable of the same range will fit and do the job. Don;t throw the old motor away, though - pass it onto someone for fixing!