There are 2 spindle bearings AND a separate bearing assembly supporting the top pulley which has radial loads on it from the belt. It is much more likely to be from where the noise emanates.
There has been a thread somewhere where the whole assembly has been rebuilt to have 2 bearings. Attached are the drawings, which I have no idea of how sound the design is, but might help.
My spindle has done close to 2000 hours, and most noise I had was from the belt not running in the center of the pulley.
Careful shimming of the motor bracket will solve this.
I have never dismantled the spindle. Only the pulley assembly, which drives the spline.
When lightly loaded extra noise can come from the spline rattling, particularly if the too in the spindle is heavy, acting like a flywheel.