Hey, well lenses are focusing and when you have the image stabilization on you're going to hear the noise of the lens focusing plus the stabilization. The rattle or clunking sound in your lens is normal. What you are hearing is the Image Stabilizer disengaging from the optics after stabilizing the glass elements in the lens. Aside from this, if you hear any other type of sound when the lens is mounted on the camera it is likely the autofocus or aperture. But if what you hear is something abnormal as if the lens is broken or so, you'll have to send them for repair.
You can contact them directly from here: https://www.sonypencoed.co.uk/contact/all-other-products/
