Could it be VR in action? How long have you been using that lens? The VR of that lens is slightly noisier compared to other VR lens
It has a mechanism that locks and unlocks the "floating" element when VR is activated/deactivated.
Look through the viewfinder and observe if you can see abnormal movement while the VR is in action. There shouldn't be any.
If there's abnormal shaking or photos are a bit blurr, time to send for servicing.