The aperture mechanism makes a clicking noise when adjusted and is not a malfunction. This sound can be picked up by the microphone of the camera when recording movies.
If the clicking sound is very noticeable, it is recommended that an external microphone with a 3.5 mm diameter mini-plug be used. This can eliminate the clicking sound caused by adjusting the aperture. Maintaining a distance between the microphone and the lens may reduce the clicking sound. Alternatively, if you do not need to record sound with the movie, you can set the Audio Recording option to Off in the menu to disable the camera microphone.
NOTE: If model-specific information is needed for how to turn off the Audio Recording option, refer to the instructions supplied with the product. Manuals are posted on your model support page.