Originally posted by MJKoski Yea the SR mechanism activates even when not in use to get sensor locked to correct position. Sony A7x with IBIS does the same thing though it is somewhat more silent.
I've done some basic tests and it's makes the noise regardless of whether shake reduction is on or off. It makes the same noise when I press the AF button. This is in full manual mode so I don't think it's related to focus.
Basically this noise is not noticeable when shooting with normal ambient noise, but is really noticeable in quiet conditions. It has a kind of mechanical sound, and ends with a small clunk that feels if something is moving back into place.