I'm living in a house 3.5 years old. Over the last 2 months I've starting having a problem with one bathroom sink. It's located on the main floor. When using the hot water faucet at about 1/2 open, the pipes hammer. The pipes are hammering in the bathroom itself. It does not occur on the cold water side... only the hot. Does anyone have an idea what the problem is? I'll be attempting to fix this problem on the weekend. I hope I do not have to replace the whole faucet. If you have any ideas on how to approach this problem... I would appreciate your advice.

Thanks,
=Warren