Do I need a Schottky diode as a flyback diode with PWM @ 30khz?
Yes, you should really use a diode with fast reverse recovery.  A Schottky is a obvious choice at this low voltage.  Schottkys have effectively instant reverse recovery for your purpose.

The lower forward voltage of the Schottky will also cause less backwards EMF on the inductance during the off time, making the overall system more efficient.

I see there is some discussion about comparing the PWM period with the reverse recovery time.  This is not really relevant since with fast enough PWM the diode is forward-conducting during the whole off interval.  The recovery time issue occurs at the start of the on time.  Until the diode turns off, it looks like a short across the load.  This is bad for the switching transistor, bad for the diode, and wastes a lot of power.

I saw a case once where the switching transistor got blown out because a slow recovery diode was accidentally installed in a motor driving application.