Cast iron sink with wall mounted faucet. The house is 75 years old, the plumbing may be that old too. The pipes are galvanized. The faucet has no identifying marks. There has been no trouble or changes in the plumbing until this started about 3 weeks ago.
When I turn on the hot water faucet about 1/4 turn, a medium flow for doing dishes, there is a loud groaning sound and vibration. If I open the faucet more about 1/2 turn, a high flow for filling a pot, the vibration and sound goes away. I can turn the water on just a little bit to allow a tiny drip without any sound or vibration.
Is this water hammer? Can water hammer just start happening one day and can it occur when a faucet is partially opened and then stop when the faucet is open all the way?
What could be causing this and how can I stop this vibration and groaning?