Answer to: Camera clicks when focussing with the app.Sounds like the image stabilization gyro is faulty . Or definatly a mechanical part is failing or has failed in the camera itself. If it was me I would definetly take it back we're you bought it and show them was going on. I highly dought it's just a software problem causing the camera to make noises.
Answer to: My nokia Lumia 520 camera lens is scratchedI don't think it easy to replace a camera lens,however,check the Nokia Lumia 520 User Manual to see if that could work:http://www.manualbirds.com/manuals/nokia-lumia-520-user-manual-612738