I've got a 1953 single-story house, with all copper water piping. When turning on the shower upstairs, there is frequently some serious water hammer. I'm familiar with water hammer that goes "bang" once when opening or closing a valve, but this makes a extremely loud, repetitive banging, sort of like a machine gun or jackhammer. It usually doesn't stop until the valve is fully opened.
The shower has two separate hot and cold valves, and they open fairly slowly (I think they're gate valves). What might be causing this, and how can I fix it? It is pretty severe, and it sounds like it will cause damage sooner or later.
EDIT: ok, so after some research, it looks like this "jackhammer" water hammer is pretty common, but I still don't know what causes it... I'd love to understand better.