I have a new two story house. When ever we run the water upstairs we hear water tappings sounds coming from the floor joist space between the first and second floors. We have been in this house for 1 1/2 years and there is no leaks that we can see. The sound typically starts a few seconds after turning the water on upstairs and lasts for a minute or so even though the water is still running.
What would be causing this sound?