just checked my configuration file for my Smoothieboard (i set current in my firmware) and all my steppers are set to 1a I think i turned them down a little. when it's higher they would constantly buzz, they were originally set to 1.68 (as per max rating on the datasheets for the stepper motors) then turned down to 1.4 then finally set to 1a where there is no noise and it still has plenty of holding torque. I always set the Bulldog extruder to the same settings.

the drivers on the board are the A9482, when I was using ramps I used the A9488's and later the DRV8825's all of them were set to 16 microsteps.

does it skip stepps when there is no filament in it ?