I recently acquired this lens and have a few questions. The image quality at both ends of the focal length is great. How long should a zoom like this take to focus? I read reviews saying that this lens should focus fast, what is fast on a zoom? When it focuses, it sounds like a robot. I have loud lenses, but this makes a grinding sound sometimes like it needs some lube or new bearings or something. Is it possible/worth it to get fixed for a reasonable price? It all seems to be functioning properly but with minor cosmetic flaws such as the noise. Thanks!