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A: The knocking sounds are what’s known as water hammer, caused when water flowing in pipes suddenly shuts off and vibrates with enough force to cause the pipes to knock against wood framing.

“It can create a water hammer. We didn’t want to do that in the cold weather, which already stresses the pipe,” he said.

When a larger volume of steam is colapsed by colder water, the bang or banging is much louder and is called water hammer.

Such a "water hammer" has tossed pipelines as much as a kilometer, Cenovus's Fagnan says, leaving them sticking out of the ground like toothpicks embedded more than three meters deep.

The "water hammer" produced by the quick acting valves of elevators has always been objectionable, both in its effect at the pumping-house and upon water mains and connections.