Just like with fireplaces, the underground water sounds sometimes don't continue if you ALT TAB out of game and back in. Additionally, I exited a tunnel with the sounds and left to go south up a hill...and the water tunnel sound continued long after leaving the tunnels.

Go into tunnel, ALT TAB a few times, sometimes it disappears when coming back, sometimes it stays. And just today, the sound continued to follow me far away from the water sources.