When playing back movies, sounds that were not heard during recording can be heard.
Sounds produced by the lens or the camera may have been recorded.
If the sound is noticeable, use an external microphone with a mini-plug 3.5 mm in diameter. By connecting it to the microphone jack of the camera and placing it as far away from the lens as possible, the sound can be considerably reduced.
If the sound still bothers you, you can record movies without audio by setting Audio Recording to Off, or setting Audio Rec Level to the lowest sound level.