Heat dissipation could become critical, because so much more voltage is dropping across the transzorb compared to simple diode! This alone could be a motivation to connect the transzorb to motor terminal and not to ground as shown in one of the examples I gave you. As the free wheeling current is flowing through the transzorb only during a fraction of period, heat dissipation is limited to some extent. In any case the current rating of transzorb must equal the maximum current rating, of course. Start with a turn-on voltage of transzorb of a few volts and see what happens refering to torque and noise, and to heat dissipation!!
At the start where you might not have the needed transzorbs you could put some free wheel diodes in series. This should give you at least a tendency whether it works (reducing the noise and increasing the torque).

Kai