Love of lathes.

[Refugee]

I would wire the original motor up off load and power it at 110V for a couple of hours and see if it all runs in and quietens down. The movable parts in the brush gear perhaps need looking at too as if there is anything with slack in it there will be noise. The noise should stay well below the sound of the jointed belt anyway and you have also established that a non jointed belt will not fit.