Note 4 camera buzzing?

I just bought a second hand Note 4, but there seems to be an issue with the camera. Sometimes when i want to take pictures and i start the camera, there's a weird buzzing sound and the image shown on screen is a bit blurry and i have to leave it a few seconds or shake the phone to make the buzzing dissappear, and the camera to start showing images properly. This doesn't happen very often though, and no matter what it will still take good pictures afterwards. Should i be worried? I'm guessing it's the OIS, should i consider replacing the camera in the near future? Or the OIS is different hardware than the camera?

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