DRV8811: Spike noise on motor current

Part Number:DRV8811

Hi,

Our customer has been testing the DRV8811 with a stepping motor.
He has observed the current of motor windings.
The waveforms of the current is as follows.

There are spike noises on the current waveforms.

I have some questions.

 What is the cause the spikes generate?

 Is it affected by "cogging"?

Thank you in advance.

Best regards,

Takishin