The sound is very much like the sound when you turn on Live View mode. It makes the sound when I tilt the camera up and down. I can not replicate it all the time. I will pay attention to whether it is a specific lens or not. It is not the auto focus sound, I dont think. Thank you for your help. Any other ideas?
Is there any chance you are inadvertently pressing the preview button on the lens mount? That would cause the lens diaphragm to stop down and then open back up when when you release the button. That might cause a slight sound.
I think you might be right! How embarrassing. I have chunky, large hands and that might be what has been happening. Stupid preview button. It is definitely the sound I was hearing. Thank you! I will post again if it turns out that wasn't it. So far it looks like the solution.