Originally posted by cdw2000 I am certain that the OS is off and the clicking is coming from the AF. It sounds like I got a defective lens. I put an inquiry in to Sigma as well.
I would recommend that you alert the seller to the problem, and that you return it. You will most likely have other options in the future, and you would not want to bother to take the chance of having to keep it and just experience failure after failure. One time I purchased a 50-500 and the focus was almost dead slow. I immediately contacted the seller and returned it.
So, as I said, contact the seller, get a return of your cash and save it for a real reliable lens that you can enjoy.
Have a nice weekend.