Water Hammer

During the summer months over the past 3 years a water hammer situation has developed, from what I do not know. It sounds like bang, bang, bang in rapid sucession and sometimes it repeats but with less force like an echo. It has to be damaging the pipes (All copper soldered). I would expect a water hammer if water was being shut off in the house somewhere but that is not the case. I called the local water authority and they said they had no idea what it was, yea, right. What could be causing this and how do I fix it????