Start-up Noise - K-5 IIs

Picked up my new camera last week. Last night, for the first time, I noticed that the aperture actuator in the camera body makes a brief buzzing noise when I first turn it on, or when it wakes up from sleep mode. With the lens removed, I can see that the aperture actuator moves slightly when this occurs.  The behavior is consistent and repeatable everyone, but I didn't notice it previously.  The actuator still seems to function properly as the lens stops down during exposure or with the optical preview.

Is this normal K-5 behaviour that I just didn't notice before, or is something I should have Pentax look at (obviously, still within the warranty period)?

Thanks in advance!