Why is my recently refurbed Kitchenaid Professional 6 mixer so loud?

Why is my recently refurbed Kitchenaid Professional 6 mixer so loud?

I recently refurbished my Kitchenaid Professional 6 mixer by replacing the plastic gear box with a metal one, as well as replacing the motor and worm gear. Now it’s loud. Real loud. There’s no screeching or grinding, just an uncomfortable loudness. I’m positive it’s the interaction of the worm gear with the motor, as I removed the other gears from the gearbox and it’s just as loud as when it’s fully geared.