Have they always done this or has it just started? If it used to be quiet you might check your gibs to take out any slop.

I downloaded the manual and since this doesn't have a software interface it will be difficult to walk you through. Parameter p009 is the gain setting, I would check what the current value is and then lower by 1 or 2 save and test. If you inadvertantly change other settings you could reduce system performance and possibly make the drive unusable.