Is the whining at the PWM frequency or the step frequency? Is it possible your motors are on and the noise is just the current regulator doing its thing but no steps are performed? Is the step pin connected to the controller properly? If you put a resistor+bicolour led (reverse-parallel red+green) across each stepper winding, do you see both the LEDs changing color at the step speed?
If the whining is the step frequency, the problem is they're just stalled. Slower! Since you have a low supply voltage, the current in the steppers can't react very fast (dI/dT=V/L) so you can't achieve a high step rate, and your torque curve will drop right off at pretty low speed.