[Blackhawk]

I have an 2nd floor sink faucet that has started causing a knocking sound in the wall when only the hot water is running. This started a couple of months ago. It is a two handle faucet and only the hot water side is causing the problem. It only starts knocking after the handle is opened past about halfway. The entire bathroom was remodeled about 4 years ago with copper pipe. The faucet is a high quality well known brand. After doing a little research on this forum, it sounds like this is being caused by a fluctuation in pressure in the pipes, which is not water hammer. If I understand correctly, water hammer occurs after a faucet or valve is shutoff. I read one thread that talked about the possibility of a faulty washer causing the pressure fluctuation. The water runs fine with normal volume up until that halfway point. Is the faucet really the most likely cause of the knocking? What signs should I be looking for inside the handle valve?